The stability analysis method of hydrodynamic journal bearing system based on non-linear oil film force was presented, in which the approach to determine the stability of the system and the mathematical calculating method were introduced. A dimensionless Sommerfeld number was utilized to express the system synthetical parameters. By the Sommerfeld number, the stability and the dynamic characteristics of hydrodynamic journal bearing system can be easily calculated, and a dimensionless stability map of a rigid and symmetrical journal bearing system was presented as an example.