In order to use the post-install pullout method to test the compressive strength of fiber cement mortar and simulate the status of reinforcement, synthetic fiber (polypropylene fiber and polyvinyl alcohol fiber) cement mortar and steel fiber cement mortar were used to reinforce plain concrete blocks, respectively. After the reinforcement, post-install pullout testing of the reinforced layer was carried out to obtain the pullout force. Based on the relationship between the representative value of the pullout force and the representative value of the corresponding compressive strength of fiber cement mortar test cubes, a fitting strength measurement formula was established using the discrete least squares approximation method. Results show that the accuracy of the strength measurement formula was high and the effectiveness of the strength measurement formula was validated in practice. The incorporation of steel fiber has a better effect on the increase of the pullout force than the synthetic fiber. According to the strength measurement formula, the post-install pullout method can test the fiber cement mortar on-site when the compressive strength ranges from 20 to 90 MPa.