In order to obtain a highly accurate tunable microwave signal source, the Sagnac ring is formed by using an erbium-doped fiber as a saturated absorb e r as a laser single longitudinal mode selection element,and a single-mode Bril l ouin laser of a double ring structure is formed with the Sagnac ring and the ann ular cavity Brillouin laser.A high-precision temperature control system with s e ries double PID control is designed.By adopting the series PID algorithm,the c losed-loop negative feedback structure is used to realize the high-precision a nd stable temperature control.When the temperature rises from 26℃ to the target temperature of 40℃,the steady-state time is about 35s,and the overshoot is 0. 1%.The temperature control system is used to control the temperature of the Bri llouin laser gain fiber.When the temperature changes from 25℃ to 85℃,the mic rowave signal output of 11.04to 11.106GHz is obtained.The slope of the signal frequency and temperature is 1.1MHz/℃,when the pumping wavelength is changed f rom 1528nm to 1565nm,a tunable microwave signal output of 11.04to 10.77GHz is obtained.