Aiming at the quantitative judgment of synchronous sampling of sinusoidal signals and the quantitative evaluation of synchronization error in asynchronous sampling, an evaluation and judgment method based on four-parameter fitting is proposed, which can avoid the point counting error of 1 that affects the resolution during synchronization judgment. On this basis, the quantitative evaluation of synchronization error is defined and realized. In the actual sine wave, square wave, and triangular wave acquisition and measurement experiments, the correctness and feasibility of the method are verified. After using single-frequency digital filter processing, it can be extended and applied to the synchronous acquisition of non-sinusoidal periodic signals. The method described in this paper can be used in the quantitative evaluation of synchronization characteristics of acquisition and measurement systems with high synchronization requirements, and can also be used in quasi-synchronous sampling and measurement to quantitatively give synchronization deviations for compensation and correction of measurement errors.