In order to work out the measuring method of noise factor of microchannel plate, a method to measure the noise factor of microchannel plate by measuring the sensitivity of photocathode and signal to noise ratio of image intensifier is proposed. According to this method, the noise factor of microchannel plate is measured under different cathode voltage, microchannel plate voltage and anode voltage. The results show that the noise factor of microchannel plate change with the change of cathode voltage, microchannel plate voltage and anode voltage. The voltage of microchannel plate has the greatest influence on noise factor and the anode voltage has the least. When the voltage of microchannel plate is increased by 100 V, the noise factor increases by about 0.11. The noise factor increases about 3.3×10^-4 for every 100 V of anode voltage. The increase of working voltage of microchannel plate means the increase of electron collision energy and the increase of secondary electron emission coefficient. According to the existing noise theory of microchannel plate, the noise factor of microchannel plate will be reduced, but the measured results are increased. The reason for this contradiction is that in the existing noise theory of microchannel plate, only the influence of secondary electron emission coefficient, detection rate and electron collision probability on the noise factor are considered, but the influence of collision electron energy on the noise factor is not considered, so the noise theory needs to be revised.