The relationship between radiation absorption and temperature was analysed with climate space diagram based on climate space theory. The results show the climate space of the tomato in the solar greenhouse can be divided into three sections. When the temperature is below 16.7℃ and above 28.3℃, the radiation absorption has a great difference compared with that of the black body, and the warp is bigger when the temperature is below16.7℃ than above 28.3℃, and the data fluctuates greatly. When the temperature is 16.7～28.3℃, which is close to the most suitable temperature, the radiation absorption of the tomato is closer to ideal black body radiation. The climate space diagram of the tomato in the solar greenhouse is quite similar to that of the cardinal studied by Gates D. M, whereas sun radiation the tomato absorbs is lower than that of the black body.