Numerical Hankel transform for circularly symmetric system at variable sampling intervals in input and optput planes is presented. An improved hybrid algorithm by using quasi Gradient Decent algorithm and spectrum selectivity is applied to the design of pure phase elements (PPE) in uniform illumination. Considering heat conductivity the simulated result shows that 97.2% of the incident beam energy is homogeneously concentrated into the desired focal spot in the target plane, and it fits to the required profile with the top profile error 1.1%.