The three-dimensional (3D) measurement speed of optical-sectioning structured illumination microscopy (SIM) has always been an important factor in the application of this technology. Present 3D measurement methods require at least two exposures at the same axial position to obtain the sectioned image. A 3D measurement technique based on single-exposure SIM is proposed. Firstly, one SIM image is taken at each axial position, and there is a certain phase shifting between the fringes of adjacent axial positions. Then the axial light intensity curve corresponding to each pixel is analyzed, the axial modulation curve is calculated, and the peak value is located. Finally, the 3D reconstruction result of the sample can be obtained through calibration and scaling. Experiment proves that our method can obtain 3D result as accurate as the traditional optical sectioning method, with the measurement efficiency and image processing efficiency greatly improved.