Abstract: The efficiency of dielectric reflection grating was calculated with C method theoretically.Characteristics of the photoresist grating mask were obtained from SEM pictures and the curves of grating efficiency were presented.The trend of these curves had some relationships with correspondent masks' characteristics.So,a nondestructive testing method with the characteristic spectrum of efficiency to estimate the groove of grating was put forward.It is concluded that this method is useful to determine whether the photoresist has been developed to the basement which is the key in manufacture technology of grating mask.