While 27% of the Universe is made of dark matter, the particle identity of the dark matter still remains a mystery. Collider studies offers a complementary tool to explore the nature of the dark matter, in addition to dark matter direct and indirect detections. In this talk, I will discuss the collider studies of the dark matter, focusing on how to observe dark matter signals, and how to distinguish dark matter scenarios. I will cover the model-independent approach for the monojet/monophoton plus missing ET signals, as well as model-dependent signatures of dark matter produced in the cascade decay chain of parent particles.