In high numerical aperture and low technic factor lithography process, degradation of the image quality because of the coma aberration in the projection lens has become a serious problem. Fast and accurate on-site measurement of coma aberration is required. A novel on-site coma measurement technique based on linewidth asymmetry of the aerial image is proposed. Compared with the resist-based coma measurement techniques, the technique based on the aerial image possess the advantage of time-saving. The simulation results of PROLITH show that the measurement accuracy of the technique is better than 1.4 nm. The accuracy increases approximately 30 percent and 1/3 measuring time is saved compared with the TAMIS technique. Using the technique, the coma of the projection lens on PAS5500 scanner of ASML is measured. The experiment shows that the reproducibility of the coma measurement is better than 1.2 nm, and this technique can meet the requirement of the high-accuracy coma measurement.