The increase in atmospheric nitrogen (N) deposition is an important aspect of global change. Numerous studies have shown that longterm N deposition would increase N: phosphorus (P) of ecosystems, leading to the increase of P limitation in ecosystems and hence accelerating the P demand of plants. In this paper, we conducted a 2year (2013-2014) N∶P supply (10 g·m^-2·a^-1 N combined with different P amounts) potcultured experiment for a common desert steppe species Pennisetum centrasiaticum. We determined the effects of N∶P supply on C∶N∶P stoichiometry in both soil and P. centrasiaticum (leaves and belowground parts). We also analyzed the indication of C∶N∶P stoichiometry for the growth and nutrient utilization of P. centrasiaticum. The results showed that：（1） reducing N∶P supply (thereby increasing P fertilization) significantly decreased C∶P and N∶P in both soils and P. centrasiaticum, alleviating P limitation for the growth of P. centrasiaticum, and further promoting the biomass accumulation of P. centrasiaticum. （2） The gradual decrease of N∶P supply would shift P limitation to N limitation for P. centrasiaticum. （3） In this case, P. centrasiaticum increased the ability of N resorption from its senescing leaves, which reduced its dependence on soil N pool, reflecting the adaptation of P. centrasiaticum to Nlimited environments. Our results suggest that appropriate artificial P addition could adjust the stoichiometry balance of C, N, and P between soil and plants, alleviate the pressure between soil P supply and plant P demand, and thus mitigating Ninduced increase of P limitation. The results could provide scientific guidance for the adaptive management of fragile ecosystems under increasing N deposition.