In this paper we discuss the design of computer-based haptic graphs for blind and visually impaired people with the support of our preliminary experimental results. Since visual impairment makes data visualisation techniques inappropriate for blind people, we are developing a system that can make graphs accessible through haptic and audio media. The disparity between human haptic perception and the sensation simulated by force feedback devices is discussed. Our strategies to tackle technical difficulties posed by the limitations of force feedback devices are explained. Based on the results of experiments conducted on both blind and sighted people, we suggested two techniques: engraving and the use of texture to model curved lines on haptic graphs. Integration of surface property and auditory cues in our system are proposed to assist blind users in exploring haptic graphs.