The opto-structural system of an engineering space optical remote sensor project was studied.The temperature field of the opto-structural system was discretely expressed with temperature level,axial gradient,radial gradient and circumferential gradients group.And its dimension instability was expressed with the changes of position,equation parameters and roughness of optical surfaces of primary and secondary mirrors.The relationship between temperature field change and dimension instability was discussed.Results suggested that the influence sensitivities of temperature level and gradients are different each other.