In order to meet the development requirements of miniaturization and low cost of missile-borne radar seeker, a multi-serial port servo controller based on DSP serial port expansion is designed. Through the development of DSP serial port multiplexing function, the hardware resources of only three groups of SCI transceiver registers are used to complete the transceiver of three-way sensor data of azimuth and elevation angle, angular velocity and one-way host computer data, and the design of two-dimensional servo control system based on single DSP architecture is realized. The FPGA related circuit and software design are simplified, which provides technical support for the low cost and miniaturization of the servo controller. The experimental results show that the system is reliable, stable and suitable for engineering applications.