Abstract: An experimental study is made on reinforced concrete specimens with round section under combined action of axial force and bending. The reinforcement strain, crack width, crack width-load and reinforcement stress-load relationship at various load levels are measured and the development of crack is monitored. Experiment results show that the development rule of cracks is basically the same for all kinds of specimens, that there is no cracking in the specimens when load is small, that from the first crack appearance in concrete to the yield in reinforcement, crack width increases approximately according to linearity with loading, and that after reinforcement yield, crack width increases rapidly with loading. The probability distribution of crack width is established based on test results.