Supercritical water gasification technology provides a promising way for the efficient and clean utilization of high-sodium Zhundong coal. Pore structure evolution rules of char in the gasification process can provide important information for the heat and mass transfer in char particles and the optimization of kinetic models. In this work, supercritical water gasification experiments of Zhundong coal were conducted and the increase of temperature was found to promote the hydrogen production and gas yield increasing. Residual chars were characterized using techniques of nitrogen adsorption at 77 K, mercury intrusion porosimetry and micro-computed tomography. The results indicated that pores mainly appeared in two regions of 1.7-2 nm and 600-2000 nm. The specific surface area showed an increasing trend in the gasification process with micropores dominating the total surface area. The increase of temperature promoted the pore volume development, and a good linear relationship between pore volume and gas production was found.