The calculation of factors of the Fourier of function of two variables with the help of the biquadratic spline-interpolation, based on the spline-interpolation. In digital processing of two-dimensional signals there is a task of effective calculation of factors of Fourier of two variables. In the given article the algorithm of approximate calculation of factors of Fourier of functions of two variables with the help of parabolic spline-interpolation constructed on the basis of a spline-interlineation is researched. The classical methods of construction of interpolation splines have lacks: the additional boundary conditions and additional knots for odd degree (except for knots of interpolation) require. For construction of the system of basic quadratic splines, the methods are used which do not require the definition of additional boundary conditions and additional knots (except for knots of interpolation). The error of an offered method is researched.