In order to realize the stable control of the Mach-Zehnder modulator (MZM) operating bias point, a simple and effective control scheme based on the average optical power slope value detection was proposed. Firstly, the importance of MZM operating bias point stable control was analyzed. Then, the feasibility of the control algorithm was studied from the perspective of mathematical theory derivation. Then, the simulation verification was carried out by Matlab. Finally, the experiment of the MZM operating bias point stable control system was carried out on the built platform in the laboratory. The results show that this is a simple and effective ditherless bias control technology suitable for various modulation formats, and the experimental observation results show the performance of bite error rate of the system did not drop within 72 hours and maintain at 10-9, effectively ensuring the reliability of the modulation system MZM operation in laser communication.