A terahertz imaging system based on active ghost imaging method is proposed. The system can achieve high speed and high resolution imaging using one single-pixel detector, breaking through the resolution limit of terahertz devices. Reusable measurement matrix is obtained by the rotation of double random amplitude plates so that the imaging speed is greatly improved. The influence of imaging distance, size of random pattern, sampling number and the relativity of sampling matrix on imaging quality are numerically analyzed. The best parameters are used for experiment. And the motion strategy of double amplitude plates is optimized. Experimental results show that the imaging resolution is 4 mm when the wavelength of terahertz source is 3 mm, and imaging speed is determined by the motor of amplitude plates. The feasibility of terahertz active ghost imaging method is proved.