Abstract: This paper studies the thermal lensing effect of optical element under laser heating at non-thermal equilibrium state. The experiment of time sequence observation of laser orientation angel for transmitting laser beam through an optical element under heating of powerful laser has been carried out. It has been found that before thermal equilibrium to become established in the element, its thermal lensing effect presents a kind of behavior of fluctuation. The authors have also provided a preliminary explanation for this phenomenon and pointed out its practical sense.