Professor Fu Baopu analysed many data of precipitation about mountains in China and foreign countries, and suggested a famous experimental formula to express the relation between the precipitation P_z and the altitude z. It is usually as follows: where P_h-the precipitation at the foot of the hill, h-the height at thefoot of the hill, a and H (the height with the maximum precipitation of the mountain) are two parameters decided by regions and seasons. The original method to calculate these two parameters from observatioa data of mountains is a gradual approach method which searches the better solution, step by step and by eyes only.