The combination of steel tube and core concrete can be strengthened by installing studs (internal studs) on the inner wall of the steel tube of the concrete filled steel tube (CFST) member. Taking core concrete strength, stud diameter and length as the main parameters, the push-out tests of 8 CFST specimens with studs were carried out. The results show that the load-slip curve of the CFST internal stud specimens consists of four stages: elastic stage, elastoplastic stage, load decreasing stage and load residual stage. When the stud shear failure load reaches the maximum, the concrete does not appear cracking and crushing phenomenon. The core concrete in the tube will not separate from the steel tube during the core concrete being pushed out. The ultimate slip value of studs in CFST specimen decreases with the increase of core concrete strength, increases with the increase of stud diameter, and less affected by the length of studs. Based on the analysis of the test results, a formula for calculating the ultimate slip value of the inner studs is proposed.