Abstract: The wavelet transform is a major way to process the optical information. A filter designed according to the wavelet function is put on the Fourier plane in an optical 4f system, the way which is an usual solution to implement optical wavelet transform. A grating was taken as the filter of the system to implement the optical wavelet transform. The grating and the whole system were designed according to the relationship between the grating parameters and the wavelet threshold function, and by the aid of ZEMAX software. The simulation result shows that the wavelet transform can be implemented with the grating as the filter of the 4f system, and the grating can character the wavelet functon.