At present, all bearing plates used in plate loading test(PLT) are rigid, which leads to a certain error in deformation modulus of the foundation soil due to without considering the actual distribution of the compressive stress under the plates. In order to realize a uniform load under the plate, a flexible bearing plate has been invented through the installation of an air bag under the traditional rigid bearing plate and has been proved applicable for PLT. During the PLT using the flexible bearing plate, the internal deformation of the air bag can be measured with the help of the inductance meter and the self-made sensor; and the load value at all levels is controlled by the resultant P and the air pressure p simultaneously. The indoor comparative test results show that the tested using the rigid bearing plate is about 14.0% larger than ones by using flexible bearing plate. The finite element method simulation also shows that the tested using the rigid load bearing plate is at least 10% larger than ones using the flexible load bearing plate; and an accurate can be get using the flexible bearing plate. So it can be concluded that the testing method for the foundation soils deformation modulus using flexible bearing plate is feasible and advanced; and the cost and efficiency can be fully accepted.