Lunar laser ranging (LLR) has the characteristics of far measurement range and small number of return laser photons, so the position of detector receiving return photons should be adjusted properly during LLR observation to improve the detection success probability. Synchronization control system for multiple step motors is researched and realized with the technique of field programmable gate array (FPGA), and control interview program is developed with VC++ software developing instrument. Finally, computer control of the detector position is realized on xoy detecting plate. Test result indicates that two step motors can run separately or simultaneously, so that the detector could move along x axis or y axis alone, or along x axis and y axis at the same time. The minimal step length is 2.5 μm, which allows for precise detector position control.