The streak cameras which with an internal or external microchannel plate (MCP) image amplification has a significant enhancement on the detect signal threshold, but also induces the saturation effect of MCP to limit the dynamic range of streak camera. The saturation effect of MCP is described through the channel multiplier model of a discrete resistance capacitance dynode chain, explaining that the input output linear range of MCP which in both the two amplification method is depend on the charge restored in the channels the contribution of compensate effect which comes from the bias current is very limited, even using a low restistance MCP in the external method streak camera, so the streak cameras with an internal and external MCP image amplification should have equivalent dynamic range, low resistance MCP only function if a rapid sequence shots is required, and MCP gain was set up properly is critical for the dynamic range of streak camera.