Abstract: Reasonable support timing plays an important role in maintaining the stability of roadway surrounding rock and ensuring the safety of mine production. Taking the unloading chamber of Zhongjiu Iron Mine as the engineering background, considering the effect of temporary support,the range of permanent support timing ( temporary support without permanent support area length ΔL) was preliminarily selected based on the convergence-constraint method,which broke through the traditional convergence-constraint method. It can only be applied to the determination of support timing for roadways without temporary support. Furthermore,the variation trend of stress,displacement and plastic zone of surrounding rock is analyzed by FLAC 3D numerical simulation,and the best permanent support time is obtained. According to the field monitoring results,the support effect of surrounding rock is evaluated,and the rationality of the selection of permanent support time is verified. The results show that the temporary support structure has a certain influence on the solution results of the surrounding rock characteristic curve and the longitudinal section deformation curve of the surrounding rock. The maximum deformation of the surrounding rock of the roadway after considering the temporary support is 666. 86 mm. When the timing of permanent support is different,the pressure and deformation of surrounding rock-support structure are also different. With the increase of ΔL,the pressure and displacement of surrounding rock-support structure decrease and increase respectively. By calculating the maximum surrounding rock pressure that the permanent support structure can withstand,ΔL>1. 07 m is obtained. Through the in-situ stress release rate,ΔL =8. 50 m is obtained. Combined with numerical simulation,the timing of permanent support is determined to be 6 m. The actual monitoring data show that the displacement of the roof and floor and the side of the unloading chamber is 84. 73 mm and 190. 82 mm,respectively. The surface displacement of the surrounding rock of the chamber is within the controllable range,and the supporting effect is good. The research can provide theoretical and practical reference for the determination of the permanent support time of related roadways.