In this paper, we use the Fokker-Planck equation, which is derived from the Master equation and has a diffusive fluctuation term, to discuss three chemical models' fluctuation under different situations. We point out: the fluctuation near equilibrium is local and Gaussian; as the system deviate from equilibrium, the fluctuations appear correlative at different points in space; Schlogl's trimolecular model has non classical exponents; but Schlogl's dimolecular model has classical exponents. The diversification of these fluctuations is determined by the property of the system itself. By the method used in this paper, we can treate these problems in a unified base, and, therefore, provide a solution to the question about critical exponents presented in the literature[6].