Lithium slag (LS) from lithium mica is the fastest growing solid waste in the Jiangxi Province of China in recent years, and a suitable utilization method has not been found. In this paper, the effects of LS on the physical and mechanical properties of white reactive powder concrete (WRPC) were investigated. The microstructure of the WRPC with LS was studied by SEM and TG-DSC. When the LS content was 8%, the flexural strength of the WRPC at 28 days increased by 6.4%. When the content of LS was 11%, it reduced the wear of the WRPC by 54%, dry shrinkage by 21.7%, and electric flux by 15.6%. A content of lithium slag within 11% did not significantly affect the Hunter whiteness. Lithium slag has a certain degree of pozzolanic activity, which can play a chemical-filling role in WRPC and effectively improve the microstructure. Lithium slag reduced the early hydration of WRPC, but improved the late hydration process. This work shows that lithium slag can be used as a high-quality green admixture in WRPC and can solve the problem of lithium slag occupying land resources and polluting the environment. This approach, therefore, promotes a clean production process for the lithium industry.