Optical switch is the key function unit of fiber delay line, which will be influenced by optical switch. A whole digital temperature control system based on TMS320F2812 digital signal processor (DSP) of Texas Instruments (TI) Co. is designed to control the operating temperature of micro-electronic mechanical systems (MEMS) optical switch, which utilizing DS18B20 to collect temperature and then sending it to DSP. In the DSP difference between the temperature to be measured and the temperature set as the input of proportioral integration differential (PID) algorithm, so control quantity produced through calculation is used to control DRV592 as to drive thermal electric cooler (TEC). This system has the characteristics of simple hardware circuit, high integration, high precision. The error of this system is ±0.1 ℃, temperature control domain is 0 ℃～70 ℃, so the optical switch can operate regularly.