A main machine frame of a punching and grinding tester by high speed underwater steel ball method is provided with a steel cylinder, and the inner part of the steel cylinder is provided with a stirring impeller driven by a speed regulation motor; the steel cylinder is also provided with a test piece supporting plate for placing the piece to be tested, and the lower side of the test piece supporting plate is provided with a water-collecting tray; the bottom of the water-collecting tray is provided with an elevator, which is characterized in that the speed regulation scope of the speed regulation motor is between 500r/min-10000r/min; the stirring impeller of the product is composed of an upper impeller, a lower impeller, two pieces of side blades and one root of mixer shaft; the external diameter of the upper impeller is 5-40mm larger than the external diameter of the lower impeller. The two pieces of side blades are in P shape, and the largest widthes at the upper portions of the two pieces of side blades are respectively greater than the largest widthes of the lower portions. The punching and grinding tester increases the stirring impeller rotating speed and changes the combination of the stirring impeller shape and the punching and grinding medium dimension, thereby obtaining higher near underflow speed and increasing the punching and grinding efficiency. The equipment has features of reasonable structure and convenient operation.