To investigate the model of fatigue crack growth rate da/dN based on crack tip opening displacement (CTOD) as the driving parameter, the variation ranges $Δ δ_{M}$ $Δ δ_{M}$ by linear elastic fracture mechanics and $Δ δ_{G}$ $Δ δ_{G}$ by geometric principle of CTOD were deduced. The fitting relationships of $Δ δ_{M} - d a / d N$ $Δ δ_{M} - d a / d N$ and $Δ δ_{G} - d a / d N$ $Δ δ_{G} - d a / d N$ were attained through da/dN experiment by taking 17Cr16Ni2 stainless steel, and their discrepancies were compared. The results showed that at the early and middle periods, the relationships of $Δ δ_{M} - d a / d N$ $Δ δ_{M} - d a / d N$ and $Δ δ_{G} - d a / d N$ $Δ δ_{G} - d a / d N$ could be expressed by Paris law, and da/dN driven by $Δ δ_{M}$ $Δ δ_{M}$ was faster than that by $Δ δ_{G}$ $Δ δ_{G}$ notably; at the later period, the experimental data of $Δ δ_{M} - d a / d N$ $Δ δ_{M} - d a / d N$ and $Δ δ_{G} - d a / d N$ $Δ δ_{G} - d a / d N$ deviated from the fitted Paris curves and were above them with being crossed with each other; in the total variation range of CTOD, it was better to fit the relationships of $Δ δ_{M} - d a / d N$ $Δ δ_{M} - d a / d N$ and $Δ δ_{G} - d a / d N$ $Δ δ_{G} - d a / d N$ by polynomial method rather than Paris law.

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