In the development of hydrocarbon reservoirs, the qualitative classification of the reservoir plays an important role, and predicting the high-quality horizons of the reservoir reduces production costs and increases productivity. In general, the qualitative study of the reservoir is done using the porosity and permeability data obtained from the core and well drilling diagrams and their adaptation using the hydraulic flow unit method. According to the information in this article, a three-class problem is defined to check the quality of the Gar reservoir. These three classes, including low, medium, and high reservoir quality, are defined using effective porosity and Gamma ray at well locations. Then, using seismic data and appropriate attributes, a tree dimensional model of this three-class will be extracted. To apply the algorithm, seismic data of one of the reservoirs of southwestern Iran has been used. The main reservoir zone of this field is the Gar zone, which itself includes three zones, zones 1, 2, and 3, which should be examined in terms of reservoir quality. The results of applying the method and obtaining 3D model of the quality of reservoirs using seismic and well data showed that zone 2 of the Gar reservoir has a higher reservoir quality than zones 1 and 3, and in many parts of this zone the quality of the reservoir is high.