With the microscopic phase-field model, the early precipitation mechanisms of the ternary Ni75AlxV25-x alloys with middle Al composition were explored by computer simulation in this paper. Through the simulated atomic pictures and composition order parameters of precipitates, we can explain the complex precipitation mechanisms of theta (Ni3V) and gamma' (Ni3Al) ordered phases. Simulated results also show that the precipitation characteristic of gamma' phase transforms from non-classical nucleation and growth to congruent ordering + Spinodal decomposition gradually, otherwise, the precipitation characteristic of 0 phase transforms from congruent ordering + Spinodal decomposition to non-classical nucleation and growth mechanism gradually.