Fiber coupled semiconductor lasers are mostly used as the pump source of high-power fiber lasers,which are very sensitive to the current fluctuations.In order to ensure the normal wavelength and output power,a high stability constant current source circuit is designed.The constant current source circuit adopts closed-loop feedback control to make the MOS tube work in the amplifier area to output constant current.The thick film resistor with through-hole is used as the sampling resistor,which has high voltage resistance,wide resistance range and strong heat dissipation ability,which greatly improves the stability of the constant current source circuit and realizes the adjustable 0~20 A current.In view of the long opening and closing time of general constant-current source circuit,transistors are added between the op-amp and the MOS tube to amplify the signal and shorten the opening and closing time of the circuit.At the same time,analog switching circuit is added in the design to accurately control the signal.The experimental results show that the constant current source circuit takes 4.5 ms and 6.5 ms to turn on and off respectively.The constant current plate structure has strong and stable heat dissipation capacity,good high temperature resistance and high current stability,reaching the magnitude of 10-3,when the power supply designed by this circuit is used as the laser power supply of the fiber coupled semiconductor laser,the central wavelength and output power of the laser are relatively stable.