Abstract: On the basis of Kirchhoff approximate equation, a new approach - GRACO (Graphical Acoustics Computing) is developed for forecasting the echo characteristics of underwater targets in real time. Using 3D graphic processing system, the geometrical model of complex underwater target is established. Basing on OpenGL, the geometrical model is transformed into the visual image on the computer's screen, and target surface's normal vector and space included in the information of pixels are obtained. Instead of computing the surface integral directly, the forecast of echo characteristic of underwater target is achieved by calculating the sum of the contribution from all the pixels in the screen image. Numerical results show that GRACO method enjoys high precision and computing speed is 9 to 10 times faster than the Planar Elements Method.