Abstract:The feature of the size-of-source effect (SSE) in low temperature measurement differs from that in high temperature measurement. A correction formula for the SSE in different source sizes and different background radiations is derived. It is from a calculation model at a suppositional detector temperature which can avoid the influence of background radiation on the SSE measurement. Theoretical analytical expression for the SSE in different source sizes are obtained, and the rule of the novel model and classical high temperature model are different at the source temperature lower than or near ambient temperature. The formulae and conclusion are suitable for the SSE correction for a temperature measurement at an arbitrary temperature.