This study is to understand the structural behavior of flexural member according to the splice length of specimens reinforced by GFRP reinforcing bar. As compared with reinforcement, GFRP reinforcing bar has superior material properties such as non-corrosiveness, light weight, non-conduction, etc. However, GFRP reinforcing bar is difficult to use instead of reinforcement owing to brittle fracture when it failed. Therefore, GFRP reinforcing bar mixed with deformed reinforcing bar were used. A total of 5 specimen was produced and tested and the test main variables are the diameter of tension steel, lap splice length of GFRP reinforcing bar which are for investigating the reinforcement effects. The diameter of tension steel set as D10, and D13 and the lap splice length of GFRP reinforcing bar set as 30db, 45db and, 60db. The results of the experimental test, the specimen with GFRP reinforcing bar proved more reinforcement effect than the one without GFRP tie bar. At the same time, the specimen with tension steel of D13 increased an overall strength more than the one with tension steel of D10. The longer lap splice length showed increase the strength.