With homemade highspeed visualized shear viscosity test instrument as the experimental platform, taken common two kinds of lubricating oil as experimental material, the oil film in bearing clearance flow was researched as an object. By adding high polymer additive, the influence of layer loss in stability of molecular weight and concentration on concentric rotating cylindrical oil film was analyzed, and the laminar flow stability of Newton fluid and polymer dilute solution was discussed to put forward a model of simple effective viscosity. The results show that the polymer additive helps delay of the layer loss in stability to appear.