[en] In the present study, we applied an in situ high temperature optical microscopy (HTOM) to compare the sintering rate of fluctuating heating and isothermal heating for Al-10Mg alloy. The in situ observation found that the former one is much faster than the latter although its temperature was equal to the maximum value of fluctuating temperature field. The same result occurred in Al-Cu and Al-Zn alloy systems. In other words, these imply that a kind of heat shock activation effect (HSAE) exists in fluctuating sintering other than isothermal sintering for aluminum alloy. Further study showed that HSAE could accelerate sintering process by promoting particles melting and atoms inter-diffusing for a eutectic alloy system. So fluctuating heating is expected to become a fast sintering method for a eutectic powder system with low cost