Affected by the manufacturing process of gratings, the slight deviation of grating parameters can easily lead the coupling coefficients to deviating from the design values, deteriorating the distributed feedback (DFB) semiconductor lasers. In this paper, the coupling coefficients of lateral asymmetric gratings were analyzed by combining the coupled mode theory in the case of perturbation with numerical simulations. When the ratio of grating width to ridge width is in a certain range, the light fields in the waveguide slightly deviate due to the introduction of the asymmetric distance between two sub-gratings, thus changing the coupling of the light fields. This is beneficial for the coupling coefficients to stabilize in a reasonable range and considerably alleviates the influence of such parameters as duty ratio on the coupling coefficients. Besides, it lowers the influence of errors in the grating process on the properties of DFB semiconductor lasers. Furthermore, the uniform distribution of photon density in the resonator avoids the space hole-burning effect that easily occurs in the conventional grating structure, which is helpful for the output of laser with narrow line width from the semiconductor laser. In conclusion, this work provides a theoretical reference for the design and application of gratings with lateral asynchronous coupling.