According to the linearized three-section model of input/output power transfer function (TF), the theoretical assessment method of all-optical reshapers’ performance is investigated and verified by simulation of four-wave-mixing-based scheme. The performance of all-optical reshapers dependent on the input signal of Gaussian distribution is analyzed. The transfer function is divided into five regions from low to high power levels, and a larger improvement of quality factor or BER performance can be obtained for the cases that the average level of mark pulses exists in the fifth region. With the increase of the TF′s second-section slope for a desirable reshaper, the gain saturation of quality factor or BER performance will occur and the extinction ratio will be improved linearly.