The invention discloses a testing device for inhibiting dithering of a speckle image under an aerobic environment with high temperature of 1200 DEG C. The device comprises a light-weight high-temperature ceramic plate, an orthogonal quartz lamp heating array, a light-pervious window, a light-weight ceramic thermal-insulation frame, speckle particles, a panel test piece, a quartz glass square frame, a thermal-insulation light-pervious channel, a light-pervious hole, an MOS camera, a band pass filter, a lens and an image processing computer. In a high-temperature heat test, the temperature rises, the density of hot air decreases, the hot air moves upward, and the difference in upper and lower air densities in a heating area causes an unsteady change in the refractive index of the air to cause dithering of an image, so that the correlation analysis of a digital image fails. In order to obtain a clear image of surface deformation before heating, the invention comprehensively adopts multi-level multi-segment space sealing and area isolation measures to inhibit dithering of the hot air in an effective transfer path of optical information, thereby obtaining a clear speckle image of surface deformation of the part before being heated in an aerobic environment with high temperature and the full field deformation of the heated surface.