As the local oscillator of the space optical clock, the ultra-stable laser determines the short-to-medium-term frequency stability of the space optical clock. Considering the space station's restrictions on load weight and volume, as well as the impact of vibration and shock during launch, a tunable external cavity diode laser with small size, stable structure and no elastic adjustment device was developed. Optimized the design of the structure of the optical path board, developed small optical components, and developed a double-sided optical path system based on this. Experimental tests show that the free-running line width of the laser is about 175 kHz, which can run stably and reliably for a long time. At the same time, considering the deformation of the optical path substrate in the space microgravity environment, the topology optimization design of the optical board was carried out. Through mechanical simulation analysis, the maximum deformation of the optical path substrate under the influence of gravity is 0.43 µm, which initially meets the requirements of space applications. © 2020 SPIE.