Abstract: The Triassic Baikouquan formation in the western slope of Mahu sag, Junggar basin is a set of fan-delta front sandy conglomerate deposits. Conventional post-stack wave impedance inversion can’t be used to distinguish effective reservoir and tight reservoir, which constrains well placement and reserves calculation. Analysis on the available elastic parameter crossplots obtained from logging data shows that vp/vs ratio is an effective elastic sensitive parameter to classify tight reservoir and effective reservoir. Based on accurate calculation of shale content, effective porosity, water saturation and other parameters, a reasonable petrophysical model is selected and the accuracy of S-wave velocity estimation is improved significantly, which could provide fundamental data for prestack inversion of elastic sensitive parameters in the study area. With the optimized parameters of vp/vs ratio, effective reservoirs can be identified and exploratory well success rate can reach 80%, which provides basis for well placement and reserves confirmation in the study area