Abstract: With the continuous development of astronomical technology, remote observation and autonomous observation have gradually become the mainstream trend of astronomical observation, and the automatic focusing technology has been paid more and more attention.The electric focuser is an indispensable accessory equipment of the astronomical telescope, and it is the key equipment for remote observation and autonomous observation to realize automatic focusing. In order to realize the automatic focusing of the 10 inch Meade telescope at Lijiang astronomical observatory of Yunnan Observatory, we developed a set of small telescope electric focuser, designed the relevant control circuit, developed the serial communication protocol, and wrote an open source ASCOM driver-SS focuser. This paper introduces the structure principle and realization method of the electric focusing device in detail. The experimental results show that it has good stability and fully meets the design requirements. It provides the experience and method for the design of the astronomical electric focuser.