The current research on self-injection-locking frequency comb theory is incomplete in exploring the influence of different parameters on self-starting effect. The results of the operating-point locking theory used to explain the locking mechanism and numerical simulation are quite different and cannot explain some experimental phenomena well. Based on the Lugiato-Lefever Equation (LLE) taking into consideration of the backscattering effect, a self-starting Kerr microcomb model is constructed. The influence of key parameters in the model on the self-started locking state of the frequency comb are discussed by using the numerical simulation based on split-step Fourier method and combining the physical connotations of the parameters. Then from the basic formula of the model, the operating-point locking theory is modified to overcome the inadequacies of the self-injection locking micro-comb theory. It is demonstrated that the modified theory can improve the accuracy of the prediction of the locking state in the self-starting numerical simulation, as well as the compatibility between the theoretical prediction and the numerical simulation or experimental results.