The effective stress range (ESR) and the number of stress cycles (NSC) are two key parameters in fatigue damage evaluation. The inaccuracies in predicting remaining fatigue life can be attributed to either one of these two parameters. A sensitivity analysis is described to address the effects of four cycle-counting methods on ESR and NSC for various fatigue details, which including rain-flow counting (RF), mean-crossing-peak counting (MCP), level-crossing counting (LC) and simple-range counting (SR). Using field monitoring data under normal traffic of Wei River Bridge, the comparative results of four methods showed that RF was more conservative than MCP and SR. The relationships between RF and other three counting methods were determined in the form of a correlation coefficient and a linear regression line. Therefore, values obtained for ESR and NSC by MCP, LC and SR can be converted to values for RF, which is used for comparison and transformation of fatigue life evaluation results using different cycle-counting methods.