A “Two Times Thermal Irradiance and Four Times Measuring Method” for measuring the emissivity of the object was proposed. According to the instrument developed independently, the method and design has the advantage to measure the irradiance of the thermal irradiance which is exactly the same as that which is irradiated to the measured object. The method not only improve the measurement accuracy, but also can be designed as a small size portable emissivity tester. Designing of 1000w / m2 or more strong heat radiation source, the signal to noise ratio in equipment is increased substantially. In order to compensate for the warming of the measured target under the strong heat radiation source, the universal expression of solving the emissivity in the non-isothermal system and a "Process Method" for compensating warming were proposed, which solved the bottleneck problem caused by the temperature change in the non-temperature system. The comparison of the three measurement results of the emissivity measurement method shows that the method proposed in this paper is superior to the other two methods.