Abstract: The technology of air curtain load reduction at launcher mouth is a technology of jet load reduction when launching an object under water. The influence of the parameters of jet on the load an attitude of the object in the process of unloading the launcher needs to bu tested an studied. In order to reduce the technical and economic risks before the full-scale test, the scale test of appropriate proportion is usually carried out first. In this paper,that isobaric model similarity method for underwater launch process and air curtain jet process is put forward by using theorem and equation analysis method, and compared with traditional decompression model, it is pointed out that the isobaric model can more truly simulate the process of full-size underwater air curtain injection, and more accurately reflect the load and attitude law of full-length object under the technology of air curtain load reduction at the launcher mouth.