The invention provides a measurement device for simultaneously measuring ash content and water content, which comprises a case, a radioactive source and microwave transmitting/receiving antenna, a measurement table, a detector, a microwave receiving/transmitting antenna, a microwave source and a computer, wherein the measurement table is positioned above the radioactive source and microwave transmitting/receiving antenna; the microwave source is connected to a microwave network, and the microwave network is connected with the microwave transmitting antenna and the microwave receiving antenna respectively; and the computer is connected with the detector and the microwave network respectively, and the computer measures the ash content of a material according to the ray attenuation information detected by the detector and measures the water content of the material according to the ray attenuation information and the microwave attenuation information. The whole material sample is scanned and measured by using gamma-ray attenuation measurement technology to obtain average mass and thickness of the material sample, and the water content of the sample is corrected and calculated by usingthe mass and the thickness so as to greatly improve the accuracy of water content measurement.