An approach is proposed to analyze the two- and three-photon absorption process using the open-aperture Z-scan technique. The normalized transmittance equations of one pulse energy presented here can be used to investigate the effect of different temporal profiles of excitation laser pulses on the nonlinear absorption coefficients (NACs). The numerical simulations show that our method is well in accordance with the usual Z-scan in determination of two- and three-photon absorption coefficients in 0.6–1.0 ranges of nonlinear energy transmittance for the typical pulse models, such as Gaussian, ${\mathrm{sech}}^2$, Lorentz, and asymmetric ${\mathrm{sech}}^2$ models. Our results suggest that the introduced parameter in relation to the pulse envelope in the approach may become a candidate for the parameters taking account of the NAC deviation from the pulse profiles of the probe laser.