In order to solve the problem that in the underground rock mass, the horizontal stress is difficult to be estimated, a crack stable condition based on a model with two collinear cracks was established, and validated by experiments. The results showed that the crack stable condition is effective. By using this condition, the range of horizontal stress was evaluated, and the results agreed well with the in-situ measurement results. Finally, the phenomeon that the ratio of horizontal stress to vertical stress is scattered in a wide range near the underground surface, but scattered in a narrow range in the deep zone, was explained well by this result.
