The invention provides a supporting device and a portable ultrasonic impact gun provided with the same. The supporting device is provided with a ball screw mechanism and a sliding seat driven by the ball screw mechanism to slide. A guide rod front bracket and a guide rod rear bracket are fixed to the sliding seat. A pair of guide rods is connected between the lower portion of the guide rod front bracket and the guide rod rear bracket. The two guide rods both support an adjusting seat. A supporting seat is fixed to the adjusting seat. A front-back locating hole matched with the corresponding position of a gun body is formed in the supporting seat. A pair of buffer springs is arranged between the upper portion of the guide rod front bracket and the supporting seat. The front ends of the two buffer springs are inserted into corresponding adjusting holes in the guide rod front bracket correspondingly. A fine adjustment bolt used for pushing the corresponding buffer spring is arranged in each adjusting hole. According to the portable ultrasonic impact gun, the middle portion of the gun body is arranged in the locating hole of the supporting seat to be fixed; impact abrasion between the gun body and the supporting seat can be reduced through rubber rings or rubber gaskets; reciprocating impact vibration can be effectively buffered through the buffer springs; and accordingly, the operational stability is improved.