All-optical logic gates are the basic unit of all-optical computer and all-optical network in the field of communication in the future. A variety of structures and methods has been proposed for the implementation of all-optical logic gate, however, the bottleneck of this technique has emerged, which is how to cascade the individual all-optical logic gates to achieve more complex logical relationships. The existing schemes for all-optical logic gate, generally, don’t have excellent cascade to realize multilevel connection. And the existing analysis on the cascade usually stays on the theoretical level without combination with the realistic situation, which have little sense for the practical application. This work has presented a novel ultrafast all-optical NOT gate based on high nonlinear Sagnac interferometer, has built its mathematical model and digital model, has adopted Gauss pulse as input light for simulation, which is more realistic, and has analyzed the system cascade on the basis of simulation results. The analysis of cascade has taken into account the influence of fiber loss and walk-off effect. The basic conclusions in this article show that the proposed scheme of all-optical logic gates can maintain excellent cascade under practical situation with interference factors.