The evaluation of oil productivity in unconventional reservoirs with complex fracture networks is essential in practical design for improving the production performance. A three-dimensional unified pipe-network method (3D UPM) is developed to understand oil flow behavior in fractured unconventional reservoirs by considering the compressibility of both fluids and solids. Governing equations for transient pressure analysis are discretized based on a pipe equivalence technique. The complex flow transfer between the rock matrix and fractures is solved using the superposition principle at the media interface, greatly simplifying the matrix-fracture coupling process in the 3D pipe-network system. The results, calculated in an implicit time scheme, are verified against commercial software COMSOL to demonstrate the reliability of this method for evaluating well performance. A single multi-fractured horizontal well (MFHW) is numerically investigated to evaluate the influences of natural/hydraulic fracture numbers and properties on the well productivity, which also indicates the necessity of using a 3D model for oil production simulation. Finally, a double MFHWs system was adopted to analyze the influences of fracture networks formed by the interconnection between natural fractures and hydraulic fractures, demonstrating that natural fractures greatly contribute to high well productivity.