The thermo-sensitive point and the thermo-sensitive stage for fertility alteration in the thermo-sensitive genic male sterile (TGMS) line Annong S-1 were studied. In nature environment and green house,the leaf, root and young panicle were treated by low and high temperature respectively. In total, 8 treatments were carried out. Results indicated that during the thermo-sensitive stage of fertility alteration, in high temperature environmental conditions, the low temperature treatment in the root did not significantly induce Annong S-1 to be fertile, while the low temperature treatment in young panicle obviously induced Annong S-1 to be fertile. Therefore, the thermo-sensitive point of Annong S-1 is the young panicle. The stage of fertility alteration was also investigated. Results indicated that alteration occurred in the phase from the formation of pollen mother cell to the tetrad of miosis. aprt gene is related the male sterility. The expression of aprt gene in root,young panicle and leaf were investigated by RT-PCR respectively. In young panicle, the expression of aprt gene was greatly down regulated by high temperature, while in root and leaf the expressions have no great changes. These data show that the young panicle is sensitive to temperature change. The result also supported that the young panicle is the thermo-sensitive point of Annong S-1 in the fertility alteration. These conclusions can be used to direct in hybrid rice seed production.