Abstract: The reservoir heterogeneity index and grey association analysis were used to study the reservoir heterogeneity in Chang?2 clastic reservoir of the Triassic Yangchang formation of Block?A in Dalugou area of Jing’an oilfield in Ordos basin. The result shows that the Chang?2 reservoir of Block?A is totally good in quality, the reservoir heterogeneity in the east area is relatively weak than the northwest and southwest areas. The heterogeneity trend gradually becomes stronger from the east to the west. The main controlling factors are the interlayers and sedimentary microfacies. The quicker response area after water injection could be the favorable area in remaining oil distribution, where the regional heterogeneity index ranges from 0.65 to 0.75. The study also indicates that the gray association analysis is simple and fast in calculation to more accurately give the weight coefficients of each parameter. The reservoir heterogeneity index can be used to overcome the lack of a single factor characterization of reservoir heterogeneity. Combined with the Gaussian random function simulation, a quantitative characterization of the reservoir heterogeneity is also realized