Quantitative identification of effective fractures is very important for tight clastic rock reservoir capacity and seepage ability evaluation and sweet point prediction. Tight clastic rock reservoir，belonging to marine-continent transitional facies，developed in the Upper Palaeozoic of southern Qinshui basin，which was very tight because the reservoir rock had experienced complicated tectonic evolution and sedimentation. Based on the core observation statistics and log analysis，effective fractures of tight clastic rock reservoir were identified quantitatively using principal component analysis method. Results show that the fractures of the clastic rock strata of Shanxi Formation in the Upper Palaeozoic of southern Qinshui basin are effective，the formation of which is closely related to the strong uplift and denudation of strata during Himalayan period，and they are mainly late period fractures. The opening of full filling fractures is largger，and they are mainly early period fractures. Principal components of six kinds of logging parameters which are sensitive to effective fractures were analyzed. It is found that the cumulative variance contribution ratio of the principal components of Y1 and Y2 is 88.55%. Therefore，Y1 and Y2 principal component can be used to identify the effective fractures，with good recognition effect. As a result，it can reduce the dimension and the effective information of the fracture can be extracted.