Abstract: An air hammer type impact tester including a machine base having a pressure accumulation chamber with an air inlet, a straight tube vertically suspending in the pressure accumulation chamber, a test platform mounted on the machine base and having a replaceable buffer block adapted to support the sample to be tested, a hammer block moved in the straight tube to strike the buffer block against the test sample, an air pump operated to pump air into the pressure accumulation chamber, a diaphragm moved between the bottom end of the straight tube and the air inlet of the pressure accumulation chamber, the diaphragm being forced upwards by compressed air to close the bottom end of the straight tube when compressed air is pumped from the air pump into the pressure accumulation chamber, the diaphragm being forced downwardly away from the bottom end of the straight tube by air pressure when the inside pressure of the pressure accumulation chamber surpasses a predetermined value, permitting the inside pressure of the pr