Internal friction of mono-and poly-crystal pure aluminum during creep at about 1Hz was studied. It was observed in monocrystal specimens that the internal friction decreased monotonously in the early stage of creep. A significant creep time-internal friction (1/Q-t) peak was observed during the latter half of the primary creep under suitable experimental conditions. And the internal friction kept constant during the secondary。But no 1/Q-t peak was observed with polycrystal sample under similar experimental conditions .We suggest that the appearance of 1/Q-t peak is due to the increase of the damping coefficient of moving dislocations during primary creep .A specific dislocation mechanism is proposed, and the expression thereby deduced for the internal friction during creep is satisfactorily consistent with the experiments.