Sinusoidal fringe pattern is widely used in optical profilometry; however, the traditional constant-frequency sinusoidal fringe pattern reduces 3D measurement accuracy in the defocus region. To this end, this paper presents a variable-frequency sinusoidal fringe pattern method that is optimized by the measurement depth. The proposed method improves the pixel matching accuracy and thus increases measurement accuracy. This paper theoretically determines the optimal frequency by analyzing the pixel matching error caused by intense noise in a captured image; presents the online frequency optimization along abscissa and ordinate axes in the sinusoidal fringe patterns; and details the encoding and decoding to use variable-frequency fringe patterns for 3D profilometry. Simulations and experiments demonstrate that our proposed method can improve the 3D measurement accuracy and increase measurement robustness.