The invention relates to a preemptive multi-master RS485 bus communication method based on dynamic priority, which belongs to the field of coal mine safety monitoring, and comprises the following steps: S1, a bus is in a half-duplex mode, is connected with a plurality of nodes with the same frame format, and can monitor the bus while occupying the bus to send data; S2, all the nodes are main devices and have unique ID numbers and variable bus use priorities; S3, before each node sends the data, a bus state is monitored, and if the bus is busy, frame priorities are compared; S4, each node monitors the data on the bus when sending the data, sending immediately stops if the frame on the bus is inconsistent with the frame sent by each node, and delays sending; and S5, after the frame being sent by a communication node is preempted, each node adjusts the priority of the next sending according to a priority dynamic adjustment algorithm. According to the invention, the number of bus nodes isincreased, and the bus use efficiency is fully improved.