The commensurability indicates a certain order existing in natural phenomena. The commensurability (approximate periodicity) is the expansion of periodicity. In order to forecast the occurrence year of a landing typhoon in Zhejiang, a commensurable formula of three elements was used in arrangement and calculation. Thus the commensurable formula for several years in the future can be given, and the occurrence year of a landing typhoon can be judged according to the peak value of frequency of the commensurable formula. The long-term change process of a landing typhoon can be forecasted and analyzed by means of the principle and method of commensurability. The result is relatively good and is of practical significance for typhoon prevention and disaster reduction along the coast regions. Being able to reveal the interrelation of natural phenomena, the method has broad prospects in application.