This paper have studied the dependence of the effective attenuation coefficient Г on both the parameters of system（height of plane H and field of view FOV） and parameters of sea water quality（volume attenuation coefficent c

single scattering albedo ωo） based on Monte Carlo simulation technology

which leads to an approximate formula of the minimum effective attenuation coefficient for the first time. The formula shows the quantity relationships between the effective attenuation coefficient and the parameters of sea water quality in the condition（H . FOV） is large enough

and provides powerful basis for the design of the lidar system.