A theoretical quantum key distribution (QKD) scheme using EPR pairs is proposed, which is efficient and has high capacity. The scheme uses all EPR pairs except those chosen for eavesdropping checks. Each EPR pair carries 2 bits of key information, enabling high capacity. The scheme involves Alice generating an ordered sequence of EPR pairs, sending one particle sequence to Bob, and performing Bell-basis measurements on the remaining particles. Bob measures a subset of particles to check for eavesdropping, and if no eavesdropping is detected, Alice sends the remaining particles for Bell-basis measurements. Alice and Bob then compare results to verify the key. The scheme is secure against various attacks, including direct measurement, intercept-resend, and opaque attacks. It is more efficient than existing protocols like BB84 and EPR, achieving 100% efficiency in key distribution. The protocol can be generalized for multi-party key distribution. The scheme requires Bell-state measurements, which are technically challenging but feasible. The protocol is secure and efficient, making it a promising approach for quantum key distribution.A theoretical quantum key distribution (QKD) scheme using EPR pairs is proposed, which is efficient and has high capacity. The scheme uses all EPR pairs except those chosen for eavesdropping checks. Each EPR pair carries 2 bits of key information, enabling high capacity. The scheme involves Alice generating an ordered sequence of EPR pairs, sending one particle sequence to Bob, and performing Bell-basis measurements on the remaining particles. Bob measures a subset of particles to check for eavesdropping, and if no eavesdropping is detected, Alice sends the remaining particles for Bell-basis measurements. Alice and Bob then compare results to verify the key. The scheme is secure against various attacks, including direct measurement, intercept-resend, and opaque attacks. It is more efficient than existing protocols like BB84 and EPR, achieving 100% efficiency in key distribution. The protocol can be generalized for multi-party key distribution. The scheme requires Bell-state measurements, which are technically challenging but feasible. The protocol is secure and efficient, making it a promising approach for quantum key distribution.