Microfluidics devices for separation of plasma from whole blood can be applied to numerous clinical laboratory and point-of-care diagnostics, since over 90% of blood diagnosis tests are conducted using plasma. This paper proposed a structural design of microfluidic channels for blood plasma separation. The Euler-Euler Laminar Flow Model in COMSOL Multiphysics has been utilized to simulate the blood flow behavior in microchannels. Micro chips with separating microchannels of different designs were fabricated and tested. The geometrical effect of microchannels on plasma separation was investigated. Simulation results show that curved channel contributes little in lateral migration of cells in low flow rate and becomes a difficult choice in the case of high flow rate due to the coupling of centrifugal migration and Dean Vortex. Studies on the bifurcation corner radius and the angle between main channel and side channel show that an abrupt change in flow direction of cell free layer helps to get more plasma with higher purity. An optimal design of multi-bifurcation separator has been achieved by balancing the flow resistances of the side channels and the main channels.