The utility model discloses weighting devices of a belt conveyor, and the belt conveyor and a plurality of feed inlets above the belt conveyor form a multi-material belt weighting system. The weighting devices of the belt conveyor are characterized in that a plurality of sets of the weighting devices are arranged, and each set of the weighting device comprises a metering carrier roller and two weighting sensors, wherein each weighting sensor transmits weight signals to the integrating control instrument of the multi-material belt weighting system and belongs to a digital weighting sensor. The digital weighting sensor has the characteristic of dust explosion prevention and is particularly suitable for occasions that the distance between the weighting sensor and a calculation control instrument is longer and the plurality of feed inlets form the multi-material belt weighting system. When one of the two weighting sensors in each set of weighting device has failure, the utility model can automatically switch to only use the weight signals of one sensor, and the integrating control instrument carries out multiplication processing on the weight signals of the sensor.