The invention discloses a grain moisture measuring instrument. The grain moisture measuring instrument comprises a main control board, a measuring board, a function key board, a power supply motor driving board and a signal collecting and detecting device; the measuring board, the function key board, the signal collecting and detecting device and the power supply motor driving board are electrically connected with the main control board separately, the main control board is electrically connected with the signal collecting and detecting device through the measuring board, and the power supplymotor driving board is electrically connected with the signal collecting and detecting device; the signal collecting and detecting device is internally provided with a first motor, a second motor, a temperature collecting probe and a humidity collecting probe, the humidity collecting probe is used for detecting the capacitance value in grains, and the signal collecting and detecting device comprises a first roller and a second roller. By means of the grain moisture measuring instrument, the material moisture content of particles of different diameters is detected, the cost is reduced, juice inthe grains on the first roller and the second roller is conveniently cleaned away, and the accuracy of the subsequent detection is facilitated; meanwhile, after the first roller and the second rollerare washed with water, quick drying can be facilitated, the subsequent measurement of grain moisture is facilitated, and the measurement efficiency is improved.