In the course of luminescence enhancement investigation of ZnO films coated with Ag the authors discovered that enhancement by surface plasmon resonance takes place only under low enough pumping level while under a high pumping level only quenching is observed. For interpretationof this effect simplified mathematical model describing influence of surface plasmon resonance on near band edge luminescence in ZnO is proposed. Proposed model is presented by set of rate equations considering particularly increasing of exciton recombination probability and losses depended on pumping level. These losses most likely should be of Joule’s type. Experimental dependences of excitonic luminescence intensity of ZnO films coated with Ag on pumping level appear to be close to simplified theoretical ones based on this model.