Abstract: The distributed optical fiber sensing technique has unique advantages in monitoring and inspecting of linear engineering,such as long distributed sensing and being easy to be fixed in the molded structures.The basic principle of the Brilliouin optical time domain reflectometer(BOTDR) and the technique to fix the sensing optical fiber in prefabricated piles are presented.The formulas for the distortion and internal force of the piles under the distributed strain mode are deduced,and the test results and the origin of the test error are analyzed through practical examples.The research results show that the pile strain distribution tested by the sensing optical fiber,laid in the prefabricated piles by slotting and sticking it with epoxy,can help to obtain the pile axis force,skin friction,end-bearing resistance and pile bearing features.The test error can be eliminated by setting comparative optical fiber,raising position-setting precision,consummating the sensing techniques,filtering wave,and denoising,among others.