The invention provides a method for calculating a relation between jet speed and air entrainment amount, particularly relates to a method for calculating the air entrained into water by free jet whencarrying out study on water-air two-phase flow and belongs to the field of environmental hydraulic test. The method comprises the following steps: step one, presetting the size of a jet pipeline and the size of a nozzle according to the power of a jet water pump and roughly calculating the jet speed; step two, roughly estimating air entrainment amount, and calculating the volume of a water storagedevice and the volume of an air collection device; step three, designing the size of a jet air entrainment amount calculation device according to the above calculation results; step four, filling water and exhausting air; step five, carrying out test; and step six, carrying out the step four again after one flow speed test is completed, adjusting the flow speed and carrying out next flow speed condition test. The invention provides a novel method for calculating the relation between the jet speed and the air entrainment amount; the devices used by the method are simple in structure, low in cost and accurate in numerical value.