Based on the response eqution of temperature-sensing element solved by means of convolution integral in time domain,the response of the element,especially its automatic average ability,is described,from which it is discovered that the output of the element at a certain time is a weighted average of the input of environmental temperature in the previous time.The weight increases exponentially as it approaches to the output time.This result is used to discuss the problems concerning assimilation of different temperature data,which is of significance for the improvement of the skill of data-assimilation.