Variable line-spacing gratings are widely used in spacial spectroscopic and synchrotron radiation devices, but their design and fabrication are difficult. In this paper, the geometrical theory of aspheric wave-front recording optics is briefly reviewed. The genetic algorithm is introduced to optimize parameters of holographic variable line-spacing gratings. In order to improve the efficiency of calculation. the integral expression of the objective function is also derived. Design example of holographic variable line-spacing gratings for position sensor is given to demonstrate the capability of this method. Holographic variable line-spacing gratings with large density gradient are fabricated successfully.