Objective  To access the effects of post length on horizontal load of cast post and core crown. Meth-ods  120 simulated roots made of polymethylmethacrylate were divided into 15 groups according to different mechanical fulcrum and length of post, made the wax pattern of post-core, casted and cemented the post-core. After saline soak, loaded these specimens on the Instron-4302 by the speed of 1　mm/min and recorded the maximum force of load. Results  The means of fracture resistance Wp11 of 7.0　mm, 7.5　mm, 8.0　mm, 8.5　mm, 9.0　mm were （94.24±12.47） N, （129.76± 19.89） N, （195.98±12.46） N, （208.88±24.37） N, （225.67±53.07） N and the means of dangerous stress ?滓°11 were 65.12 N, 93.07 N, 145.84 N, 161.58 N, 181.49 N; the means of fair stress [?滓11] were 39.41 MPa, 56.34 MPa, 88.34 MPa, 97.86 MPa, 109.94 MPa. It showed that the horizontal load of post-core crown system increased gradually with the increasing of the post length. It appeared the linear regression between the length of the post and fracture resistance and physiologic load. Conclusion  The increasing of the post length can increase the horizontal load of post-core crown system. During the pulp preparation of post-core system, the post  length should be added as much as possible