From viewpoint that the hardware and the software of special 3D terrain system must be designed by ourselves, we discuss the architecture，key techniques and their realization of a typical high speed 3D terrain system in this paper. First of all we select high speed processor INTEL i860 as kernel of the system. Then we design a special unit called' allocating tree' to solve the contention and bottleneck problem caused by mutil-tunnel outputs. Thirdly，we realize the hardware Z-buffer algorithm,by which visible surface determination can be sped. Lastly，we use mutil-frame buffer technique to support high refresh of mutil tunnels and mutil drawing bodies.