We investigate two important aspects of the terahertz imaging technology. They are the pulsed terahertz spectral imaging and the continuous wave terahertz imaging. Experimentally,we obtain terahertz images by these two imaging systems. We compared many aspects between the pulsed imaging system and the continuous wave imaging system,such as imaging mechanism,system resolution,system noise,imaging speed,information capacity,price,complexity,portability and their applications. Experimental results show that the pulsed imaging system has an obvious advantage that it can get more spectral information,on the other hand the continuous wave imaging system is simple and compact. The two systems have their own strong points,and are complementary to each other. In addition,we present an identification method based on the terahertz multi-spectral imaging technology.