An orthogonal two-frequency grating designed for the on-line inspection is proposed. The higher frequency fringes are introduced in the orthogonal direction of the original single frequency fringes, which are used to extract modulation and complete pixel matching in the inspection. The proposed grating can resolve the problem of pixel matching and phase calculation requiring different frequencies. In addition, the higher frequency fringes don′t influence the low frequency fringes used for the phase calculation, and the higher frequency fringes don′t need to be filtered. So the influence of filtering in phase calculation can be eliminated. Both numerical simulations and experiments prove the feasibility and validity of the proposed method.