This paper proposes a decoy-state method to counteract photon-number-splitting (PNS) attacks in the Bennett-Brassard 1984 (BB84) quantum key distribution (QKD) protocol under high loss conditions. The method involves a legitimate user intentionally replacing signal pulses with multi-photon pulses (decoy states). By checking the yield of these decoy states, the protocol can detect abnormal low loss, which would indicate a potential PNS attack. If the loss of decoy states is significantly lower than that of signal pulses, the protocol is aborted. Otherwise, the loss of signal multi-photon pulses is estimated based on the decoy states, assuming similar loss values. The BB84 protocol is a promising quantum information processing technique, but its practical implementation is limited by distance due to signal loss. Quantum repeaters could help, but they are not yet feasible. An alternative is surface-to-satellite free-space QKD, but it suffers from high loss, which can be exploited by PNS attacks. The decoy-state method addresses this by allowing the detection of PNS attacks through the comparison of yields between signal and decoy states. The paper explains that PNS attacks involve Eve splitting multi-photon pulses to extract information. The security of the protocol depends on the yield of multi-photon pulses being higher than the probability of their generation. The decoy-state method ensures that the yields of signal and decoy states are similar, allowing the detection of PNS attacks. The method is validated by showing that the estimated yield of signal multi-photon pulses can be derived from the decoy states, ensuring the protocol's security even under high loss conditions. The analysis generalizes to various photon number distributions and shows that the decoy-state method is effective in improving security against PNS attacks. The method is based on random sampling and can be extended to handle other imperfections in QKD protocols. The paper concludes that the proposed decoy-state method provides a practical solution for secure long-distance quantum communication.This paper proposes a decoy-state method to counteract photon-number-splitting (PNS) attacks in the Bennett-Brassard 1984 (BB84) quantum key distribution (QKD) protocol under high loss conditions. The method involves a legitimate user intentionally replacing signal pulses with multi-photon pulses (decoy states). By checking the yield of these decoy states, the protocol can detect abnormal low loss, which would indicate a potential PNS attack. If the loss of decoy states is significantly lower than that of signal pulses, the protocol is aborted. Otherwise, the loss of signal multi-photon pulses is estimated based on the decoy states, assuming similar loss values. The BB84 protocol is a promising quantum information processing technique, but its practical implementation is limited by distance due to signal loss. Quantum repeaters could help, but they are not yet feasible. An alternative is surface-to-satellite free-space QKD, but it suffers from high loss, which can be exploited by PNS attacks. The decoy-state method addresses this by allowing the detection of PNS attacks through the comparison of yields between signal and decoy states. The paper explains that PNS attacks involve Eve splitting multi-photon pulses to extract information. The security of the protocol depends on the yield of multi-photon pulses being higher than the probability of their generation. The decoy-state method ensures that the yields of signal and decoy states are similar, allowing the detection of PNS attacks. The method is validated by showing that the estimated yield of signal multi-photon pulses can be derived from the decoy states, ensuring the protocol's security even under high loss conditions. The analysis generalizes to various photon number distributions and shows that the decoy-state method is effective in improving security against PNS attacks. The method is based on random sampling and can be extended to handle other imperfections in QKD protocols. The paper concludes that the proposed decoy-state method provides a practical solution for secure long-distance quantum communication.