In the face of the problem that the current physical layer data transmission cannot separate the effective signal and noise,which causes the channel end to receive part of the outlier data,resulting in poor channel transmission encryption effect,a network physical layer transmission security encryption method based on GA-BPNN is proposed.Building a multi-slot encrypted transmission model,the key can be obtained after the channel capacity information is converted and processed through the 1 and 2 slots of the uplink communication phase.The first information security transmission is realized through decoding and packet decryption of the information flow through the 3 and 4 timeslots of the downlink communication phase.Use GA algorithm to select the transmission channel,calculate the proportion of individual fitness in the fitness of the transmission channel group,avoid the selection of individuals with abnormal fitness values through iterative processing,make the GA algorithm converge to the global,and obtain the optimal selection result.The experiment results show that the data obtained by this method after filtering is non-outlier data,and the filtering processing effect is good,and the maximum throughput is 5 000 b/s,consistent with the ideal throughput,indicating that the encryption effect of this method is good.