This paper investigates covert communication in STAR-RIS assisted NOMA systems, considering imperfect successive interference cancellation (SIC). The study derives closed-form expressions for detection error probability (DEP), optimal judgment threshold, average minimum DEP, and outage probability (OP) of NOMA users. An optimization problem is proposed to maximize the effective covert rate (ECR). Simulation results show that varying the transmission and reflection components of STAR-RIS can increase the maximum ECR. The system model includes a source (Alice), a STAR-RIS with K elements, a warden (Willie), and two users (Bob and Carol). Alice sends common and covert signals to Bob and Carol. The signals received by Bob and Carol are analyzed, and Willie attempts to detect the covert signal by comparing two hypotheses. The detection performance at Willie is analyzed, and the optimal judgment threshold is determined to minimize DEP. The performance analysis includes the outage probability for Bob and Carol, which is influenced by the power allocation factor and the number of STAR-RIS elements. The study proposes an optimization strategy to maximize ECR while ensuring the reliability of Carol and the covert performance of the network. The results show that increasing the number of STAR-RIS elements and the transmission power can improve the ECR. The analysis also demonstrates that the optimal power allocation factor is determined by the covertness and reliability constraints. The study concludes that the proposed method enhances the covertness performance of STAR-RIS assisted NOMA networks.This paper investigates covert communication in STAR-RIS assisted NOMA systems, considering imperfect successive interference cancellation (SIC). The study derives closed-form expressions for detection error probability (DEP), optimal judgment threshold, average minimum DEP, and outage probability (OP) of NOMA users. An optimization problem is proposed to maximize the effective covert rate (ECR). Simulation results show that varying the transmission and reflection components of STAR-RIS can increase the maximum ECR. The system model includes a source (Alice), a STAR-RIS with K elements, a warden (Willie), and two users (Bob and Carol). Alice sends common and covert signals to Bob and Carol. The signals received by Bob and Carol are analyzed, and Willie attempts to detect the covert signal by comparing two hypotheses. The detection performance at Willie is analyzed, and the optimal judgment threshold is determined to minimize DEP. The performance analysis includes the outage probability for Bob and Carol, which is influenced by the power allocation factor and the number of STAR-RIS elements. The study proposes an optimization strategy to maximize ECR while ensuring the reliability of Carol and the covert performance of the network. The results show that increasing the number of STAR-RIS elements and the transmission power can improve the ECR. The analysis also demonstrates that the optimal power allocation factor is determined by the covertness and reliability constraints. The study concludes that the proposed method enhances the covertness performance of STAR-RIS assisted NOMA networks.