In this paper, a new method is suggested to stabilize the frequency of semiconductor laser diode for heterodyne optical communication systems. In order to stabilize the frequency of semiconductor laser, the method of the injection current controal has been widely used, in which the laser frequency is locked to a F-P interferometer. By adding another servoloop to stabilize the output power of semiconductor laser, we could stabilize the laser frequency and the output power simultaneously and the frequency stability is improved by a factor of fice times.