As a kind of the common used structural material in solar PV system, Polycrystalline silicon had always been studied as a focus. In order to study the interaction mechanism between different laser wavelengths and polycrystalline silicon, polycrystalline silicon surface was respectively irradiated by the single pulse laser with wavelengths of 532 nm & 1064 nm in this paper. The surface ablation morphology was observed by the optical microscope and analyzed under the different laser energy density. The physical mechanism of the crack initiation of material surface was explored. The results indicate that: under the wavelength of 1064 nm laser, firstly ablation area size is exponential distribution and then fits a linear distribution with the increasing of the laser energy density .And in the wavelength of 532 nm, ablation area size is linear distribution; Thermal stress is the largest in spot center and the most vulnerable to stress damage as irradiated by Gaussian laser; Two wavelengths laser irradiation Polycrystalline Silicon mainly damage mechanism are hot melting damage and the dissociation damage caused by transient thermal shock. Meanwhile, the former is more likely to happen.