Most of the previous parameters that utilized as a crack driving force were established in modifying the parameter Kop in Elber’s effective SIF range (ΔKeff =Kmax–Kop). This paper focuses on the physical meaning of compliance changes caused by plastic deformation at the crack tip, the test were carried out under constant amplitude loading by using structural steel, and differences of several parameter ΔKeff from literature were analyzed. The effect of actual stress (load) amplitude at the crack tip on fatigue crack growth is investigated based on these test results, and improved two-parameter driving force model ΔKdrive=(Kmax)n(ΔK^)1-n has been proposed. Experimental data for several different types of materials taken from literature were used in the analyses. Presented results indicate that new parameter ΔKdrive was equally effective or better than ΔK(=Kmax-Kmin), ΔKeff(=Kmax-Kop) and ΔK*(=(Kmax)α(ΔK+)1-α) in correlating and predicting the R-ratio effects on fatigue crack growth rate.