Proposed in this paper is an effective mobility model of polysilicon thin-film transistors,which simulta-neously takes into account the number of grains inside the transistor channel,the transport properties of carriers between grains and grain boundaries and the gate bias controlling the mobility degradation effect,and adapts to the polysilicon thin-film transistors from small grains to large ones in linear region.It is found that,when the grain size Lg is less than 0.4μm,the effective mobility is mainly controlled by the grain boundaries,that the effective mobility can be improved by reducing the trap density of grain boundaries,that decreasing the gate oxide thickness may enhance control of effective mobility by gate voltage,and that clear effective mobility degradation may occur at a high gate voltage.