We have experimentally investigated variations in ellipsometrical parameters ψ, Δ, ρ, reflectivity R,surface sheet resistance p with radiation time by GW OOa laser annealing. Output power of 002 laser is 40 watts and beam diameter <~8 mm. 150 keY As+ ions were implanted to a dose of 1×10 16/cm2 for 6~8 Ω*cm(100)P type Si. The experiments discovered that t|r, A, R, 0 didn't obviously change in initial stage, but sharp decreased to the vicinity of values of the crystal silicon at 5 seconds radiation, and there were no any changes when extending radiation time. Measurements of thermoelectric couple and optical pyrometer shown surface temperature of Si has already reached about 1000 K in condition of 5 seconds radiation. The ifj, Zl-radiation time relation is similar to \ft, Zlof curves, it explains that OW OOa laser annealing has the characteristic of thermal annealing. We can understand from an abrupt turn in A, R, p curves that laser annealing of ion-implanted layer is swiftly completed during 1~2 seconds, and is not any linear or gradual process.