The structure of vertical three-wedge hydrodynamic bearings and the profile structure of bearing bores are studied by study and performance analysis of precision bearings, and the dynamic characteristics of hydrodynamic oil film of the bearings are analyzed by building mathematics model and analytic models. A criterion has been set up for judging the stability of oil film motion so that it is possible to tell if the main shaft may fail to tolerate any microdisturbance, while it is rotating in an equilibrium position(e,θb)where the reverse force of hydrodynamic oil film counteracts the external load on the shaft. Furthermore,the stability of the oil film with respect to wedge gap parameters bm and cm of the bearings is investigated by numerical simulation and programming,and the interrelation between the failure of bearings and the value of wedge gap is revealed,the variation of oil film stability factor Log(Sp) with eccentricity ε(ε=e/c) is established, and the optimum range of wedge gap parameters bm and cm is given. The investigation indicates that wedge gap parameters bm and cm are important sensitive parameters for design and fabrication of bearings; a certain ratio must be maintained between maximum wedge gap bm and minimum wedge gap cm. Otherwise oil film whip may occur and bearing stability may be lost and the main shaft has considerable sway in rotation. For a low speed vertical three-wedge bearing system,bm-cm≥0.8 μm. The results of comparative research successful examples of bearing design and fabrication indicates that selected values of bm and cm meet the stability criteria,which proves that the results of research are very useful for the design of bearings.