In this paper, a novel method, i.e., interval spline finite point method is presented to investigate the mechanical behavior of functionally graded material nanobeam with defects, which can provide some guidance for the design of nanoscale devices. The size-dependent behavior of the functionally graded material nanobeam is considered, and the defects of nanobeam is taken into account and simulated by weakening/strengthening the stiffness of the nanobeam, where the material properties are considering as interval parameters. Combing the interval mathematic and the Timoshenko beam theory, the governing equation of the defective functionally graded material nanobeam is derived based on principle of minimum potential energy and variational principle. To solve the high order equilibrium equation with interval parameters, the interval spline finite point method is proposed, where the B-spline function is adopted as basic function to guarantee the accuracy. Moreover, to obtain the mechanical response of the nanobeam efficiently, a gradient-based vertex strategy is presented. Finally, two numerical examples are given and the effectiveness of the proposed method are validated by comparison with the existing methods.