Uniaxial penetration experiments can test the shear strength of asphalt mixture effectively. In this paper, the shear mechanism of asphalt mixture was analyzed by establishing a particle flow model of asphalt mixture uniaxial penetration test. Based on the microscopic mechanism of particle flow，this paper used discrete element technique to microscopically simulate the uniaxial penetration test of asphalt mixture. The stress-strain curve of the mixture was obtained, the simulation results were validated, and then, the microscopic mechanism of the asphalt mixture in the uniaxial penetration test was revealed. This paper analyzed the effect of the penetration rate, pressure head diameter and specimen size on the test results and proposed appropriate test technical parameters based on this, which provides technical reference for the penetration test. Combined with uniaxial penetration test and unconfined compressive strength test, a method based on discrete element method to determine the asphalt mixture shear parameters was proposed. A method was provided to explore the properties of asphalt mixture by adopting the micromechanical analysis method.