The mechanisms and rules of hydrocarbon migration and accumulation in the Yanchang Formation of Honghe Oilfield in southwestern Ordos Basin are still unclear，which restricts the further exploration in this region. In this paper，a pressure-drop gradient model was derived in the situation of hydrocarbon migrating downward along faults and fractures in tight sandstone to investigate transport mechanisms of hydrocarbon entrapped in the Yanchang Formation of Honghe Oilfield and analyze the rules of their migration and accumulation based on the comprehensive analysis of geologic setting，gas logging，well-logging data and results obtained by quantitative grain fluorescence techniques. The results show that the pressure-drop gradient of hydrocarbon migration downward is Δp3 = (0.028±0.01) MPa/m along the faults，and 0.24 MPa/m along the fractures；in the case that the hydrocarbon migrates downward along the fractures firstly and then along the faults， the range of pressure-drop gradient is 0.14-0.18 MPa. In the late Early Cretaceous，the hydrocarbon was generated from source rock of Chang7 member mostly，and was driven by abnormal formation pressure to be transported to Chang8 member along the faults and fractures vertically. The hydrocarbon then migrated laterally along the microfractures in short distance，within small range and forming dendritic path，and accumulated in effective regions. Finally，favorable exploration targets found in Chang8 member of Honghe Oilfield are areas having open fractures and transporting layers superimposing each other，lithologic traps in“sweet spots”area with good reservoir physical property，lithology-structure traps with better regional lateral seal and layers with low residual formation pressure and relative low potential in overpressure zone.