Many studies have documented the effects of global warming on invasive plants, but little is known about the effects on plant invasion between day and night warming. We tested the impact of day and night warming on seedling growth and the competitive interaction between invasive and native species. Three invasive and three native species in the Asteraceae family were selected. Three warming patterns (day-, night-, and whole-day warming of 3 °C relative to the control) and the control were set in growth chambers. The results showed that night warming increased the root biomass and total biomass of native plants, while it had little effect on invasive plants, and night warming increased the root to shoot ratio of natives to a greater extent than invaders. Day warming increased the maximum net photosynthetic rate of native plants but decreased that of invasive plants, and during the night it increased plant height and respiratory rate of invasive plants to a greater extent than natives. With competition between invasive and native plants, night warming increased competitive suppression of the root growth of native species, but had little effect on the relative interaction intensity of invasive species in terms of root biomass. With the increase in night warming, invasion of the alien species in southern China may be facilitated in the future. Conclusions regarding the effects of future warming should be made cautiously because differences in day and night warming may have different implications for invasion.