In order to deal with the influence of the stability of the output optical power of diode laser (LD) on the flatness measurement accuracy of the strip laser flatness measuring instrument, a high stability diode laser constant current driving circuit, temperature control circuit and protective circuit were designed. FPGA was used as the system control core. Based on the principle of deep negative feedback, the accurate current control was achieved by the constant current driving circuit. The effective control of LD operating temperature was realized by temperature control circuit based on ADN8830. Driving current was slowly and linearly increased to preset value by improved slow-start circuit, and the slow-start time can be controlled precisely. High reliability and high security were realized by current limiting and electrostatic protection circuit. The results show that the driving current can be adjusted continuously from 0 to 75 mA, the adjustment accuracy can reach 0.025 mA, the short-term stability of current can reach 0.014% and the long-term stability can reach 0.016%. When the operating temperature is controlled at 25 ℃, the stability of the output optical power is 0.205%.