Hangzhou slope belt is an important new oil and gas exploration area in the northern part of the western slope belt in Xihu Sag. Nevertheless，its basic geological characteristics，especially its sedimentary characteristics，are not clear yet. For this reason，well logging，seismic，trace elements，and paleontological data were examined to study the sedimentary environment of Pinghu Formation of Hangzhou slope belt in Xihu Sag. The corresponding relationships of sedimentary facies with seismic facies were constructed and the planar distribution characteristics and vertical evolution law of the sedimentary system were summarized after the sedimentary features are discussed. The following observations could be made from the results：Pinghu Formation in the study area has a semi-enclosed bay environment in general，where the delta and barrier coast sedimentary systems mainly develop. The delta sediments mainly develop on the western edge of Hangzhou slope belt while the barrier coast ones widely distribute. Pinghu Formation has undergone a complete transgression-regression process. The deltas distributed continuously during the sedimentation of the Fifth Member of Pinghu Formation. Then，the deltas were inherited and the tidal flat scale was the largest during the sedimentation of the fourth Member of Pinghu Formation，which was the marine transgression. The deltas slowly expanded toward the center of the sag during the sedimentation of the Third Member of Pinghu Formation. The sea level dropped and the inherited deltas kept advancing on the western edge of Hangzhou slope belt during the sedimentation of the Second Member and the First Member of Pinghu Formation which were the marine regressions.