Abstract: According to the stress-strain characteristics of soil in flat dilatometer tests,the relationship between the test results and two indexes(shear modulus and the Poisson’s ratio) of the soil was derived based on the Mindlin’s solution in the elastic theory.Then,the theoretical formula of the in-situ initial horizontal stress σh0 and the lateral earth pressure coefficient at rest K0 were derived.Compared with the practical data of subway projects in Shanghai,the analytic results were satisfactory.