Based upon the basic viewpoints of A. Einstein on quantum mechanics and de Broglie's double wave functions principle，the wave-particle postulate and the wave-particle physical quantities postulate are presented. The wave-particle function as a free wave packet is obtained in which is involved a generalized δ-function factor as representations for the center of the extensive wave phenomena. The free wave packet is steady，not spreading with time, and is the real representation for the free particle. The wave function ψ describes the statistical ensemble. Combining the wave function with the wave-particle function gives the complete description for the single free particle.