There develops compacted sandy-conglomerates with giant-thickness in the northern steep slope of Dongying sag, which are characterized by low permeability and porosity and complicated geophysical features, and the reservoirs are difficult to be identified.More than 100 core samples from 10 wells are selected, tested and analyzed by ultrasound. Based on the analysis of the experimental data and results, we determine the reservoir physical characteristics of sandy-conglomerates in the study area and conclude that the main factors which influence the seismic velocity of sandy conglomerates are porosity and lithology, the second is the cement content,and the variation is not obvious whether the micro-fracture exists or not. When different fluids are saturated in the rocks, P-wave velocity changes slightly while S-wave velocity doesn’t change. So, in the ideal state, we can identify fluid by the ratio of P-wave velocity and S-wave velocity.The relationship between the velocity and density of the rock is relatively good when the porosity is greater than 5% while poor when porosity less than 5%.