The characteristic of Rowland circle concave gratings is analyzed with the scalar wave theory. The deviation of the image position from that predicted by the grating equation is calculated. This result can′t be obtained by the geometric ray tracing method. The calculated result of the dispersion and resolution consists with that calculated with the geometric ray tracing method. The image quality affected by the groove number, the mode size and the groove rounding is analyzed in details. The wave aberration and the ray aberration are also given.