A "two times thermal irradiance and four times measuring method" was proposed to measure the surface emissivity of any object. Compared with the previous methods, the proposed method can completely eliminate the interference of the lens and cavity walls of the sensor to measure accurately the irradiance of the observed object, implying its ability to improve the accuracy of surface emissivity measurement and making the equipment of emissivity measurement portable. The designed 1000+w/m2 strong heat radiation source considerably improved the signal to noise ratio of the equipment. To compensate the warming effect of the measured object under the strong heat radiation source, we proposed a universal expression to solve the emissivity in the non-isothermal system and a "Process Method" to reduce warming. The comparison of three measurement results showed that the proposed method outperformed the others.