Hydrological phenomena with certainty and uncertainty, have been commonly analyzed based on the deterministic methods and nondeterministic methods. These two methods have been widely used in hydrology and increasingly close to couple. This paper made a preliminary study on the coupling to the background, essence and approach. The first connotation of coupling based on hydrology deterministic methods and nondeterministic methods were given; Then the objective background of coupling was analyzed, the philosophical foundation of coupling about dialectical unity of the certainty and uncertainty, mutual transformation of uncertainty and certainty of under certain conditions were pointed out; In the end, the three main ways of coupling were concluded: (1) Simple mixing way for the solution of a hydrological problem was divided into two parts, one part is based on a deterministic method, an - other part is based on nondeterministic methods; (2) General embedded way in a general framework on a deterministic method and a nondeterministic method were embedded in order to improve the reliability; (3) Complex coupling it means mutual penetration of a deterministic method and a nondeterministic method for giving full play to their respective features.