In order to explore the effects of lithium slag substitution rate, basalt fiber length， basalt fiber dosage and their interaction on the mechanical properties of lithium slag-coal gangue solid waste concrete and realize the optimization of multiple indicators, a single-factor test was conducted to determine the optimal baseline level of each factor in the response surface methodology (RSM).Quadratic polynomial regression models were established for the 28 d uniaxial compressive strength and splitting tensile strength of concrete to determine the optimal material parameters. The results show that the optimal substitution rate of lithium slag, the length and dosage of basalt fiber in the single-factor test are 25% (mass fraction), 18 mm, and 0.16% (volume fraction), respectively. The interaction between lithium slag substitution rate and basalt fiber dosage, and the interaction between basalt fiber length and dosage, in the response surface experiments are the key factors affecting compressive strength and tensile strength, respectively. The optimal parameters obtained by regression simulation as 22.875% (mass fraction) lithium slag substitution rate, 0.184% (volume fraction) fiber dosage, and 18 mm fiber length, and shows a high degree of fit with the results of parallel tests, indicating that the regression model can provide an effective reference for the multi-objective optimization of the mechanical properties of basalt fiber-lithium slag-coal gangue concrete.