Phase transitions on a clean reconstructed Si(100)-c(8×8) surface induced by atomic hydrogen adsorption at different temperatures have been studied using low energy electron diffraction (LEED) . It has been found that: at liquid nitrogen temperature, successive dosing of atomic hydrogen cause the surface go through a series of phase transitions from c(8×8)to(4×l)-H to(2×l)-H and finally to (1×1)- H. At different temperatures from 700×3 down to room temperature, successive saturation doses of atomic hydrogen can induce phase transitions from c(8×8)to c(4×4)-H to (2×1)-H and finally to(1×1)-H.