To understand defect processes under temperature variation irradiation, Fe-16Cr-17Ni austenitic model alloy was irradiated with heavy ions by changing the irradiation temperature in a stepwise manner from 473 to 773 K and from 573 to 773 K. Most of the interstitial loops formed by the pre-irradiation at 473 or 573 K disappeared in the initial stage of subsequent irradiation at 773 K. With increasing the dose at 773 K, the size and density of loops increased again. The behaviors of loops during 773 K irradiation were influenced not only by the dose but also by the temperature of pre-irradiation. These phenomena were analyzed using rate theory for defect clustering. Numerical calculation indicated that radiation induced resolution of small vacancy clusters brought vacancy-predominant condition temporarily by changing the temperature from low to high and resulted in shrinkage of interstitial loops.