In order to solve the problem that the detection efficiency of quantum states at the receiving end is low when phase coded continuous variable quantum key distribution (CVQKD) is transmitted over a long distance,this paper proposes to use naive Bayes classifier at the receiving end to improve the system performance.NB classifier first trains quantum states of labeled categories,learns the distribution of quantum states of different categories,calculates the prior probability and likelihood probability of each category,and then calculates the posterior probability of substates to be measured belonging to each category based on the prior probability and likelihood probability,and determines the category of substates to be measured according to the magnitude of the posterior probability.The simulation results show that the improved scheme can improve the system performance by reducing the probability of the test state being incorrectly measured at the receiving end.When the excess noise is 0.01,the safety distance of the improved scheme can exceed 250 km.