The invention discloses a hidden hazardous material detecting method based on video SAR. According to the hidden hazardous material detecting method, an arc-shaped rail is arranged above a security checking area, and a plurality of radars with same working frequency in an SAR working mode are arranged on the rails; and in operation of the radars, the radars perform uniform-speed reciprocation along the arc-shaped rail and transmit a linear frequency modulation continuous terahertz wave, thereby forming an azimuth synthetic aperture image and obtaining a detected image of an object in the security checking area. According to the hidden hazardous material detecting method, the azimuth synthetic aperture image which is formed in uniform-speed motion of the radars in the arc-shaped rail is utilized for realizing long-distance real-time omnidirectional high-resolution image of the object in the security checking area, and furthermore quick imaging is performed through transmitting an electromagnetic wave with an ultrahigh frequency or higher frequency for preventing defocusing caused by object motion.