A special waveform of CCD being irradiated by intense laser is explained and simulated. Its specialty is that reference level is altered and becomes equal with saturated data level, which can answer for CCD’s black video induced by laser and named as excessive saturation effect. Alteration of reference level has been explained by signal charges injection into the measuring well during reference time. In CCD, wells barriers are largely lower than channel stop. After that all transfer wells are crammed, many remained signal charges getting rid of clock’s control can be hold in channel, and move along it in thermal diffusion and self-induced drift. They can fill up the measuring well ahead of clock’s permission and alter reference level to saturated data level. Based on the explanation, the waveform is simulated on an equivalent circuit of CCD’s charge measurement structure, which is built on the platform of Multisim2001. The voltage sources and switches are used to manipulate the charge and discharge of a capacitor, which simulates the charge injection and resetting of measuring well. The clocks controlling switches represent the injection and reset clocks in CCD. To simulate clock’s impact on output, other capacitor is used to connect it to capacitor that represents the measuring well. The equivalent circuit is validated by the simulated normal waveform. Then, altering the clock and charging the capacitor ahead, the excessive saturation waveform is simulated, which validates the explanation to excessive saturation effect.