Based on Moiré measurement technology, a method of measuring grating constant with simple setup and higher measurement precision is presented. The standard gratings with grating constants of 0.05 mm and 0.02 mm as well as corresponding grating to be measured are selected for experiments. In the experiment, three levels of Moiré fringes with high light intensity and high contrast are obtained, namely -1 level, 0 level and +1 level. The grating constant and its error of the grating to be measured are calculated. Results show that the error tends to increase with the increase of the angle between the standard grating and the grating be to measured.