The sensitivity of schlieren equipment is the key issue of the experimental results in the density measurements of fluid. A sensitivity measuring system was designed, taking a hot air gun as the disturbing region. The effect of flow velocities, temperatures of the hot air, and equipment parameters on the sensitivity of the system was investigated. The images were obtained under various temperatures and air densities. The sensitivity of the schlieren system could be characterized by the temperature variation, so called fringe number on the image. The more obtained fringe number of the image in the hot air gun disturbed schlieren imaging system, the higher sensitivity and the wider range of temperature variation. The optical paths of the schlieren imaging system were simulated by Zemax, and the experimental results agree with the theoretical analysis. The results show that the hot air disturbing method could characterize the sensitivity of schlieren equipment effectively, which provides a convenient and sensitive approach for sensitivity measurement of the schlieren system.