Phosphorus (P) is a limiting factor for productivity in aquatic ecosystems. In order to control lake eutrophication, many effective measures are taken to control the P effluent in the basin, but nitrogen (N) is difficult to control due to its complex sources. Thus, the situation of low P but yet high N effluent results in a high ratio of N:P in loading in many lakes. Plants need a suitable N:P ratio to sustain their growth, therefore, the increasing of the N:P ratio in effluents might affect the growth of submerged macrophytes. To acquire an insight into the influence of increasing N:P ratios on the submerged plants, we carried out an outdoor control experiment. Vallisneria spinulosa was planted in plastic buckets with N and P added to the buckets every 3 days. We set up five treatments with an unchanging P loading dose of 4 mg/(m²·d), with a range of nitrogen loading dose including 0, 40, 80, 120 and 160 mg/(m²·d). The experiment lasted for 80 days. Results showed that with an increase of the N:P ratio in the loading, some indicators were nearly stable, such as leaf dry weight, total plant dry weight, leaf N and total N content, leaf number, leaf P and total P content, while some other indicators, such as plant total root length, cloning stem length, stem dry weight and ramet numbers decreaed. The results above revealed that with an increasing N:P ratio in loading, individual growth indicators of V. spinulosa would remain stable or exhibit a minor increase, but that the indicators of population expansion ability, such as cloning stem length, tuber dry weight and ramet numbers, would decline, while the P absorption would not change with increasing N:P ratio in loading.