In this paper a fuzzy model for fabricating planar-gratings is given. In the model, the diffraction efficiency of the holographic grating (predicted by computer simulation) has a reasonable match with the experimentally verified results. The method can be summarized in three steps: first, a choice of the grating characteristics, which are closely related to the diffraction efficiency factors, is made; secondly, according to our experience, we construct the fuzzy matrix from the grating manufacturing parameters and the grating characteristics; finally, we use the fuzzy matrix composition to obtain the diffraction efficiency factors. Then, coupled wave theory is used to predict the diffraction efficiency. The comparisons between the results of this fuzzy model and experiments are given. It is found that the application of fuzzy set theory in grating manufacturing reduces the cost of the process and improves the quality of the grating.