Rock creep is an important factor affecting the stability of rock engineering. The long-term strength of rock

which shows an obvious size effect due to rock heterogeneity

is an important mechanical index for evaluating the long-term stability of rock engineering. The aim of this study is to investigate the size effect of long-term strength of rock. Firstly

on the basis of classical power law creep model and damage mechanics principle

a nonlinear creep damage model is established for describing the whole process of rock creep. Then

by comparing the numerical results of uniaxial compression creep test based on the proposed model with the results of indoor uniaxial compression creep test

the applicability of the model is verified. At last

numerical simulation tests are performed on seven rock specimens with different sizes under uniaxial compression creep. The size effect for long-term strength of rock is analyzed. The numerical simulations indicate that

the long-term strength of rock decreases with the increasing of size; but it will be constant when the size of the rock exceeded a specific size.