In the application of distributed optical fiber structure health monitoring, quantitative analysis of cracks is difficult. The effect of tensile, bending and folding on optical fiber and the influence degree of various factors needs to be studied. In this paper, the influence of frequency shift on optical fiber angle is tested and the effect of frequency shift caused by axial tension is compared. A new calculation formula based on BOTDA distributed optical fiber sensing is proposed and applied to crack imaging of software. The experimental results show that the change of the optical fiber angle has a great influence on the experimental results after the crack is generated, and the fracture imaging is closer to the real situation after taking the angle factor into account. Therefore, when using distributed optical fiber to monitor concrete cracks, the angle should be taken into account.