The invention discloses a variable-water-depth towing tank air-layer resistance reduction test device and method. A model to be tested is placed under the water in an experiment tank, and total resistance and local friction force of the model to be tested and advancing in the water are measured; the total resistance and local friction force of the model to be tested and advancing in the water under such state can be measured through an air supplier and an air injection device; the total resistance and local friction force of the model to be tested and advancing in the water after an air layer is diffused can stilled be measured after closing the air supplier and the air injection device; and in the process, an underwater camera system continuously records the influence of an underwater flow field. The test device and method are suitable for underwater navigation body and water surface ship model air injection resistance reduction resistance sea-keeping test; and the test technique can provide test foundation for the air-layer resistance reduction mechanism research and also can provide technical support for engineering application of a bubble boat.