Transgene escape into natural ecosystems through seed spraying or transgene introgression may potentially cause environmental biosafety problems. In this study, we assessed the environmental risk of insect-resistant transgenic rice entering farmland margins or natural ecosystems adjacent to farmland. Transgenic Cry1C* rice (T1C-19) was used to study the effects of exogenous Cry1C* expression on vegetative and reproductive growth indices under different growing conditions using the following four combined treatments of land use and weeds: farmland and uncultivated land without weeds (F–NW and U–NW, respectively), and farmland and uncultivated land with weeds (F–W and U–W, respectively). The expression of Cry1C* protein under the U–NW, F–W, and U–W conditions was significantly lower than under the control condition, F–NW. Tiller number, biomass, filled grain number, filled grain weight, and other vegetative and reproductive indices were significantly lower in the rice line TIC-19 than in MH63 under F–NW and U–NW conditions, indicating a significant fitness cost. However, under F–W and U–W conditions, vegetative growth indices such as plant height, tiller number, and biomass, as well as reproductive growth indices such as filled grain number per plant, filled grain weight per plant, and seed setting rate in TIC-19 were similar to those in MH63, indicating a long-term coexistence. These results indicate a lower ecological risk of T1C-19 compared to MH63 under F–NW and U–NW, although their long-term coexistence may lead to potential ecological risks under F–W and U–W.