With respect to the problem of light uplinks and downlinks in atmospheric turbulence, the strength of turbulence changes greatly along the path. The distribution of phase screens on the path is a vital problem to be solved in the numerical simulation of light propagation. Three different approaches: uniform distributed phase screen （UDPS）, equivalent Rytov index-interval phase screen （ERPS） and equivalent Fried parameter-interval phase screen （EFPS） are discussed. It is found that, by using ERPS method, the distance between phase screens changes automatically according to the strength of turbulence, and the fluctuation of turbulence can also be sampled sufficiently. Under the precondition that the critera for phase screen interval are satisfied, the Rytov index interval of ERPS could be any arbitrary constant value. Statistical results show that, even the Rytov index interval changes by one order of magnitude, both effective beam radius and Strehl ratio of energy change for only 2.1%. And simulated results agree well with theoretical ones. All this indicates the stability and reliability of the ERPS method.