A method for sharing reverse channel in trunk communication system includes: step A, establishing a forward channel and one or more in a group: step B, mobile stations in idle state determine a sharing reverse channel that can be used based on information of the sharing reverse channel; step C, the mobile station transmits information through the sharing reverse channel. Furthermore a system for sharing reverse channel in trunk communication system includes: channel establishing means, for establishing a forward channel and one or more in a group; reverse channel determining means, for determining a sharing reverse channel that can be used by a mobile station based on the information of the sharing reverse channel; reverse channel information transmitting means, for transmitting information through the sharing reverse channel. This invention saves the air and physics sources of the system, and reduces the collision probability of the signaling of each mobile station in idle state.