The invention discloses a three-dimensional measurement method and system based on single grating projection. The three-dimensional measurement method comprises the steps that a physical grating is projected to an object to be tested in an out-of-focus manner so as to form a sinusoidal fringe pattern, and a deformed fringe pattern of the object to be tested is collected; the deformed fringe pattern is processed by using an S-transform method to obtain the principal value phase Phi(x, y); unwrapping is performed based on a wrapping elimination method to obtain the absolute phase phi(x, y), and a three-dimensional measurement system for telecentric imaging is calibrated so as to build an imaging model, and three-dimensional coordinate information of the tested object is calculated. The three-dimensional measurement system is used for executing the method. The three-dimensional measurement method is based on the single fringe pattern, zero padding is performed on both ends of the principal value phase after the principal value phase is obtained according to the S-transform method so as to acquire up-sampling in the frequency domain, the frequency spectrum of the phase is shifted to the original position according to frequency shift characteristics of Fourier transform, a phase component of carriers is eliminated, the height-phase mapping relationship is fitted by adopting the telecentric imaging model, the three-dimensional measurement system is calibrated, the three-dimensional coordinate information of the tested object is obtained, the steps are simple, and the measurement speed is higher.