High salinity wastewater and coal gasification residue are the by-products which need to be utilized as resources for the sustainable development of coal-to-chemicals technology. Using coal gasification residue as the main raw material, supplemented with 10% Portland cement, and high salinity wastewater as the mixing water instead of tap water to prepare cementitious materials. The XRD, TG-DTG, FTIR, SEM, and MIP were used to analyze the influence mechanism of high salinity wastewater on the properties of cementitious materials. The results show that high salinity wastewater was beneficial to the strength development of the cementitious material. When 25% high salinity mastewater was used instead of tap water, the enhancing rates of compressive strength was 294%, 177%, and 186% curing at 3, 7, and 28 days. This is main due to the sulfate and chloride in the high salinity wastewater can promote the formation of C-S-H gels, Friedel's, salts and C-A-S-H gels in the hydration process of pastes, which can promote the densification of structure. The pores distribution and structure were optimized, increasing the proportion of capillary pores and decreasing macropore to promote the micro-structure more dense. This study can provide a new idea for the comprehensive utilization of industrial waste and achieve the purpose of "waste control by waste".