Semiconductor laser (LD) drive circuit required to provide enough current and working state is stable. According to semiconductor physics theory, the relationships of junction voltage, junction current and junction temperature is analyzed. Experiments on LD in dual tracking power supply constant current mode and driven by LT1912 switching power supply were made. Experimental results show that LD drive circuit of work conditions is to provide sufficient current----the switching power supply drive LD must have the output characteristics of low voltage and high power. The advantages for switching power drive LD is simple in circuit design, and working conditions are very stable. With increasing chip performance, switching power supply will be widely used.