Active accumulated temperature is an important index of agriculture heat resource in a region. In future 2×CO₂ scenario global climate will be warmer, and accumulated temperature and lasting days of china will increase. Because of simuteneous change of accumulated temperature and its lasting days after warming. the calculation of this problem is difficult. In this paper, a set of simple and practical formals are deduced based on the changing regularity of active accumulated temperature. We can take any form ouput data of GCM mean air temperature to calculate them, and the suitability is good. We also estimate the distribution of changing values of accumulated temperature Σ(≥0℃,≥10℃)and lasting days. The calculated results show that in the scenario of 2×CO₂, the accumulated temperature and its lasting days will be increased. For example. the increment ofΣ≥0℃ accumuleted temperature △ ΣT0 in north China has a trend of gradual decrease along the latitudes from 430(℃ ·d) to 240 (℃·d). In the YianZi River valley,△ΣT0 will be about 430-490 (℃·d ), but in the south, △ ΣT0 will be constent -490 (℃·d). The increment ofΣ≥10℃ accumulated temperature△ΣT10 is about 320-810(℃·d), and also have a trend of gradual decrease along latitudes. But△ΣT10 decreases in the southern coastal area of China. The increase of accumulated temperature and lasting days will be a beneficial facter for expanding the multiply-cultivated-system area, and for increasing the multiply crop index in China.