Abstract: Magnetic based capture of CTCs in microchip provides specific selection and high recovery rates with high purity.However,conventional perpendicular capture mode,which applies the magnetic field perpendicular to the flow field,shows lower capture rate under high flow field.In this paper,we suggest that the cell be captured in magnetic microchip may experience two stages which are lateral displacement stage and immobilization stage.Simulation by COMSOL and experiments were used to investigate the hydrodynamic force and magnetic force during these two stages.The data showed that the cell capture is greatly influenced by hydrodynamic force under the perpendicular capture mode.We also proposed a novel parallel capture mode design for CTC microfluidic chip.Experiment showed that this new type of chip can operated at a flow rate up to 6ml/h.