An auto-focus technology for infrared camera is researched and applied to practical project.To realize the automatic focusing,the method uses axial movement of the zoom lens,chooses Laplacian operator as evaluation function,uses optimized mountain climb-searching algorithm to judge the peak,uses PID control method to drive focus motor.And it gets an excellent result.The technology uses FPGA as the core processor and adopts the architecture of SoPC to realize the auto-focus function.The study is engineering oriented and the auto-focus system has been used in practical application.