To improve the narrow band interference(NBI) rejection performance of the adaptive wavelet packet modulation(WPM) system,an optimal wavelet packet tree(WPT) selection algorithm based on tone interference is proposed in this paper.The proposed algorithm makes use of the bit error rate(BER) and the limited transmitted signal power to construct cost function for WPT nodes,which transforms the optimal tree selection problem into the minimization of Lagrange cost function,and the optimal tree is selected by tree pruning method.Analysis and simulation results show that the proposed algorithm can accurately find the optimal tree in NBI environment and performance of the adaptive WPM system is greatly improved without sending the periodic training data.