Compared with amorphous silicon thin film,polysilicon thin film has higher electron mobility and shows better electrical properties in the device.The method of preparing polycrystalline silicon thin film by pulsed laser crystallization of amorphous silicon thin film has the advantages of low thermal budget,little influence on the substrate and low cost.An experiment about laser crystallization of amorphous silicon thin films was carried out by using 532nm solid state nanosecond laser.To solve the problem of nonuniform effect when using Gaussian beam crystallization of amorphous silicon thin film,the circular Gauss beam was transformed into a linear flat top beam based on the beam shaping system.Then the effect of single pulse energy density,pulse number and thickness of amorphous silicon thin film on the crystallization of amorphous silicon thin film was investigated.The experimental results show that,linear flat top beam show better uniformity about laser crystallization of amorphous silicon thin film.For the 100nm amorphous silicon thin film crystal,with the increase of energy density,the grain becomes larger,until the surface is thermally damaged,and the largest grain size is about 1μm × 500nm.And as the number of pulses increases,the surface roughness tends to decrease,and the minimum surface roughness is 2.38 nm.For 20 nm ultra-thin amorphous silicon film,only when the energy density is between 134mJ/cm2 and 167mJ/cm2,and the number of pulses is more than or equal to 8,the obvious crystallization effect can be observed.