The invention relates to a method for testing Young modulus, which comprises the following steps: cutting out a section of strip-shaped sample band from a smooth material and measuring the length, the width, the thickness, the weight and the density of the sample band; fixing and clamping one end of the sample band on a clamp and enabling the other end to be a suspended beam; placing the clamped sample band on a horizontal optical projector worktable and ensuring the sample band to be placed horizontally and vertically to projecting light so as to obtain the defection of the sample band in still state, that is vertical displacement; and calculating Young modulus of the sample band according to the flexural deformation deflection curve differential equation theory of mechanics of materialsand the deformation typical conclusion formula of the beam under the action of simple loading. The testing method simply and accurately measure Young modulus of materials with smaller Young modulus magnitude.