The invention provides a preparation method and application a warm-mixing agent for an asphalt mixture. The method includes the steps of firstly, dissolving sodium metaaluminate into water to obtain an aluminum-source solution; secondly, adding an alkalinity regulator into the aluminum-source solution, and stirring for 2-5 hours to regulator the alkalinity of the aluminum-source solution; thirdly,dropwise adding alkaline silicon sol into the aluminum-source solution after the alkalinity regulation to obtain a mixture, and stirring the mixture for 12-24 hours; fourthly, allowing the stirred mixture to have reaction under constant temperature of 160-180 DEG C for 20-30 hours to obtain a solid product; fifthly, washing the solid product with water, and drying the washed solid product under 50-70 DEG C for 8-12 hours to obtain the warm-mixing agent. The warm-mixing agent comprises a silicon-aluminum molecular sieve structure, and the silicon-aluminum ratio in the structure is 40:1. The preparation method has the advantages that the method is wide in raw material source and simple in process; when the prepared warm-mixing agent is applied to the asphalt mixture, asphalt mixing temperature can be lowered effectively, the water stability of the mixture is improved, and the volatilization of harmful substances is reduced.