This paper suggests an equation to estimate the total amount of prey capturedand a method to estimate the parameter of preferencewhereand also a simulation model under the existing of an alternative food species (cotton aphid)The results of predation experiments carried out in big cages can be described by following the modelAnd the more the prey species exist with one predator species, the lower the predation rate to a special prey species is.The research on the behaviour of the simulation model shows some...