The radiation exchange between the cold space (4 K) and the absolute radiometer (300 K) with wide field of view mounted on satellite is analysed when the sun is observed. That is the radiometer export radiation to space. It is equal to “minus radiation” received the by radiometer. When the field of view is wide, the “minus radiation” of absolute radiometer could not be ignored. The “minus radiation” which is full of its field of view is received, so the data measured are less than the pure solar irradiance, and the solar irradiance is the value that the “minus radiation” adding the original data. The three-step work flow chart of absolute radiometer that can measure the “minus radiation”, solar irradiance and electric compensation has been investigated. The absolute radiometer of solar constant monitor with wide field of veiw mounted on Shenzhou-3 spaceship measured solar constant in this work flow chart. The measured “minus radiation” value is equal to calculated value.