Using LED illumination formula, the light spot radius formula and the divergence angle formula of LED square array are deduced. Using fitting method, the power function formula of the spot radius and divergence angle with target distance and m value and array length are obtained.. The results show that the formulas can be quite good agreement with the numerical calculation results which the average relative error is less than 1%. It makes up for the defects that numerical method can′t analytical study on the light spot divergence characteristics of LED square array.