Computer software is more and more developed based on Graphic-User-Interface system (GUI) in order to be user-friendly program. However, this development creates some difficulties for people with impaired vision to use the computers. The "Braille Box", an assistive device, has been developed by modifying Braille cells to form a tactile stimulator array which is compatible with the fingertip. This device allows people with impaired vision to access graphic information on computer screen by tactile perception. We applied the "Braille Box" in mathematics class focused on linear graph, with visually impaired children. The result shows that they can perform task as determining the slope, the intercept and the coordinates of the intersection of two lines.