Human beings need abundant material support and energy supply in their exploration of the universe. The sustainable supply of materials is an important condition for long-term space exploration. In situ resource utilization technology (ISRU) is an important way to realize the sustainable development of space exploration, which uses the abundant raw materials in outer space to transform energy and materials. In this paper, a microfluidic reaction device based on in situ resource utilization is designed, which converts H2O and CO2 into O2 and organic matter through photoelectrocatalysis. The flow and mixing process of gas-liquid two-phase flow was studied, and both the characteristics of mass transfer and the chemical reaction of fluids in the microchannel were studied. The dynamic process of the fluid-in-microchannel chemical reaction was expounded, and a prediction model of the volumetric mass transfer coefficient was proposed. The results show that the mass transfer coefficient of the chemical reaction is affected by the gas-liquid flow characteristics, and the mass transfer affects the rate of the chemical reaction. The material conversion of in situ resources by using the microchannel device can improve efficiency and accurately control the reaction products.