The invention discloses a terminal activation detection and channel estimation method. In the cellular Internet of Things, a multi-antenna base station is arranged at the center of each cell, and a large number of Internet of Things terminal devices are distributed. In any time slot, only a part of terminals are activated and need to be accessed to the wireless network, and other terminals are ina dormant state. According to the invention, an authorization-free random access protocol is designed, i.e., the terminal can be directly accessed to the network without being authorized by the base station by activating the terminal. And at the beginning part of each time slot, the terminal is activated and a section of known pilot sequence of the base station is sent to the base station at the same time. And according to the received pilot sequence, the base station detects the state of the terminal and the corresponding channel information by using a matrix dimension reduction method. And then the equipment is activated to carry out data interaction with the base station at the rest part of the time slot. The invention provides an efficient and simple terminal activation detection and channel estimation method for the cellular Internet of Things with large-scale terminal access and a base station configured with a large-scale antenna array.