BDI index is one of the main international marine market indexes.In this paper，the mean reversion theory of BDI index“critical growth rate band”is proposed to describe the equilibrium operation law of the logarithmic growth rate deviating from the central asymmetry．Meanwhile，a nonlinear mean reversion analytical model for BDI index logarithmic growth rate based on 3Ｒ-SETAＲ is constructed．The model effectively avoids the shortcomings of the existing mean reversion models，which can not directly divide the stage threshold，and have poor accuracy，lack of robustness and application complexity．Finally，an empirical analysis of daily /weekly /monthly BDI index data from 1985 to 2015 arrive at these main conclusions: BDI index is a three regime nonlinear mean reversion process，and has a“critical growth rate band”．The daily logarithmic growth rate is mainly in the internal regime and the weekly /monthly logarithmic growth rate is mainly running in the high regime．The low regime’s and high regime’s volatility of BDI index is higher than the internal regime’s．The low regime reversion cycle is shorter，and the high regime reversion cycle is longer．