In free space optical (FSO) communications systems, the signal fading caused by atmospheric turbulence is a slow fading, so adaptive transmission technology can effectively mitigate the problem of channel fading. Considering the combined effects of turbulence, attenuation, and pointing errors on the atmospheric transmission of laser signals, we proposed an adaptive M-ary phase shift keying subcarrier modulation algorithm based on power control and studied the combined adaptation of modulation size and average transmit power. Karush-Kuhn-Tucker conditions are used to solve the optimization problem of maximizing the throughput under the constraint of average transmit power, the expressions of throughput and outage probability are derived based on Meijer G-function. We finally evaluated the effects of turbulence intensity, beam waist radius, jitter standard deviation, weather conditions, and maximum modulation order on the throughput and outage probability of adaptive system.