The water dispersible polyisocyanate(WDP) which contains both aliphatic polyurethane segment and surface active segment was synthesized by the reaction between aliphatic isocyanate and surface active polyol. The effects of relative molecular mass and dosage of polyol on the dispersibility of WDP were investigated by the phase inversion technique. Furthermore, the film formation mechanism of waterborne polyurethane coating was systematically introduced and pot life of water dispersible polyisocyanate system was analyzed by the particle size change with the time after mixing.