A transcendental function is proposed to describe laser intensity distribution, and its fitting method is given. The transcendental function which is based on Gaussian distribution function is fitted by multivariable optimization method, concretely by direction search method combined with least square method. The results show that the transcendental function is more suitable than Gaussian distribution function to describe laser intensity distribution; and the time complexity of direction search method [O(∑4i=1Ni)] is much smaller than that of traditional enumeration method [O(∏4i=1Ni)].