To explore the spreading pattern of the invasive plant Pistia stratiotes and its effects on agronomic features of rice, paddy field experiments were conducted to measure the impacts of P. stratiotes on plant morphology, biomass, competitive effect, grain yield, and soil nutrients under mixed cultivation of rice (Yundao 2) with P. stratiotes, utilizing replacement and additive de Wit series. The results showed that in mixed culture, mother ramet plant height, tiller number, biomass, and flowering plant number of P. stratiotes were obviously suppressed, and the inhibition rates were significantly higher than those of rice. The relative yield (RY) of P. stratiotes and rice was clearly lower and higher than 1.0, respectively, showing that the interspecific competition impacts on P. stratiotes were greater than impacts of intraspecific competition, whereas intraspecific competition was higher than interspecific competition in the case of rice. The relative yield total (RYT) of P. stratiotes and rice was significantly higher than 1.0 for a ratio of P. stratiotes to rice of greater than 1:1, demonstrating no significant competition. However, there was serious competition between two plants for a P. stratiotes: rice ratio lower than 1:1. The competitive balance (CB) index of P. stratiotes and rice was significantly less than zero, indicating that P. stratiotes had less competitive ability than rice. In mixed culture, rice grain yield was increased by 3.54%-13.38%, which resulted from increased effective panicle number compared with monoculture (CK). During the growth of P. stratiotes and rice, P. stratiotes consumed more soil potassium and phosphorus than rice, whereas its consumption of soil organic matter and nitrogen was less than rice; soil nutrients absorbed by P. stratiotes was obviously reduced when growing in mixed culture with rice, and there was no competition for soil nutrient utilization between P. stratiotes and rice. All results suggested that morphological and biomass characteristics of P. stratiotes put it at a disadvantage when grown with rice. Moreover, a suitable density of P. stratiotes would prevent its excessive consumption of soil nutrients and at the same time increase growth, reproduction and grain yield of rice. Thus P. stratiotes could be properly grown and applied in cultivated rice fields for the purpose of fodder use and environment purification.