A transmitting device, a transmit power control method and a control device thereof in a microwave system are provided. The transmitting device includes a transmit power control module, adapted to acquire a switching event of a modulation mode of the microwave system, and adjust a transmit power of a radio frequency transmitting module according to the switching event and a preset power control mode; and the radio frequency transmitting module, adapted to send a microwave signal to a communication peer end by adopting the transmit power adjusted by the transmit power control module. Through setting the power control module, the gain of an AM microwave system is enhanced, and the service impairment caused by the AM microwave system when actuating an ATPC function is avoided. Correspondingly, a transmit power control method in a microwave system is also provided, which enables to switch to a low modulation mode as quickly as possible without causing the service impairment when the signal is deteriorated and enhances the system gain when the signal quality is improved.