We present a lattice model of food web with alien plants invasion and analyze the model via Monte Carlo simulations and Mean Field Theory. The original food web contains herbivore, plant and detritus. Our results reveal that the alien species invasion will cause different consequences under different conditions. There are five kinds of phenomenon at most in our experiment. The system's status could be only detritus exists, only alien plants exists, all plants exist harmoniously, initial plants die out while other ingredients still be alive with the alien plants, or the alien plants become extinct while the original system keeps working. In these consequences, people should pay attention to the system collapse caused by the unsuccessful species invasion. Probably it is the reason to some ecosystems break down.