The invention discloses a heterogeneous mechanical parameter field determination method for deep rock mass paleostress field simulation. The method comprises the following steps of carrying out parameter measurement on a full-diameter core taken by a bored well in an ore field region; selecting rock mechanics parameters, and assigning for the first time; establishing a numerical simulation model of the full-diameter core according to values of the rock mechanics parameters; computing the crack density on the numerical simulation model and the crack density of the full-diameter core, when the two crack densities are approximated, making the numerical simulation model successfully calibrate the mechanics parameters of a single well corresponding to the full-diameter core, and when the two crack densities are not approximated, adjusting the assignment of the rock mechanics parameters until the two crack densities are approximated; and adopting the same method to establish the numerical simulation models of all bored wells in the ore field region, and finally, taking the rock mechanics parameter values of all numerical simulation models as input, and determining a heterogeneous mechanical parameter field of the ore field region through a sequential Gaussian interpolation method. The method is wide in application range, simple and easy and high in simulation accuracy and is suitablefor field application.