The invention discloses a microwave source power output control method for medical microwave ablation. The microwave source comprises a power output module, a voltage control module, an alarm detection module and a temperature compensation calibration module. The voltage control module outputs the control voltage in the mode of delay segmented increasing according to the external voltage V to gradually drive the power output module to output power. The temperature compensation calibration module performs one time of temperature compensation calibration on the power output module every intervalof T1 time. The alarm detection module performs one time of alarm detection every interval of T2 time. According to the control method, the problem of high power output deviation after long time working of the microwave source module can be effectively solved, and the problem of no power output because of excessively high power supply clutter at the starting moment can be effectively solved.