Yuanjiang River is an important source of diamond placer in Hunan Province, where the garnet and diamond are common heavy minerals in placer. It is of great significance for revealing the source and formation conditions of diamond placer in Hunan Province to analyze and screen garnets related to diamond. In this paper, detrital garnets (160 grains, 80 grains of DJZ-7-1 sample and 80 grains of DJZ-10-1 sample) in Chenxi area of Yuanjiang River, and inclusion garnets in diamond (5 grains) in Hunan Province were selected and analyzed by mineralogical, geochemical and statistical methods. The results show that the fluvial detrital garnets are mainly Fe-Al and Mn-Al garnet series, a few of them contain diamond inclusions. Cluster analysis, linear discriminant analysis and logistic regression analysis indicate that some G3 eclogite garnets may have genetic relationship with diamonds. Major and trace elements are certain differences between the two sites; analysis result shows that the garnets of DJZ-7-1 samples are more closely related to diamond. Based on the analysis of the Si value of detrital garnets (>3.02) and the limited temperature and pressure conditions of Hunan diamond in previous study, it is considered that Hunan diamond may be formed in the mixing area of peridotite and eclogite with a depth of less than 220 km, which is the dominant source area of lamproite-type diamond. Therefore, it is suggested that G3 garnet and lamproite should be further searched in the upper part of Chenxi, Yuanjiang River, in order to prospect the primary diamond deposits in Hunan Province.