In solar applications, collectors are usually installed with a tilt angel to obtain the maximum amount of radiation. In this paper, the anisotropic model -Hay model was used to calculate the daily total radiation on the tilt face and theoretical analysis was used to get the optimum tilt angel of southern collector face in winter months. Then the diffused radiation on horizontal face was obtained by using the isolation between daily total radiation and daily diffused radiation. Computer program was written to calculate the month radiation under different tilt angel and the maximum angel corresponding to the maximum month radiation was found. At last, the two results were compared and analyzed.