Overlay is one of key performances for modern lithographic projection systems with high-precision, a novel method for in-situ measuring the overlay performance of a lithographic system with the marks is presented. In the method, many mirror-symmetry focus calibration using alignment procedures (FOCAL) marks are printed on a wafer. The printed images of these marks are aligned by an optical alignment system and the alignment positions of the images are recorded. From the positions, overlay performance can be obtained. Through the experiments, it is demonstrated that the overlay errors, intrafield parameters and interfield parameters can be obtained with high accuracy. Compared to the XY-SETUP technique, the method avoids the dependency of measurement accuracy on the corrections of axial aberrations and makes it much simpler to perform a full-scale evaluation of a lithographic system.