The invention relates to a detection device for foreign matters on a coal conveying belt in a coal conveying system, which comprises the coal conveying belt and a microwave tomography imaging system,wherein the microwave tomography imaging system comprises an upper computer, a microwave signal transmitting module, a microwave signal regulating circuit, a 2xN microwave switch matrix, a microwave imaging sensor, a microwave signal receiving and detecting module and a data acquisition unit; the upper computer is used for providing an interface of a user interface, controlling each part of the system, transmitting data in the system, processing the data, communicating the data with equipment outside the system and the like; the microwave signal transmitting module provides microwave signals with required frequency, and indexes such as signal frequency, output power and the like are adjusted through a control interface. The detection device for foreign matters on the coal conveying belt inthe coal conveying system has the advantages that according to the method, the metal or nonmetal foreign parts in the coal raw material on the coal conveying belt in operation can be found in time, and the next foreign part removal is possible by using the detected information.