In this paper,the temporal auto-correlation properties of diffusing light in ultrasound-modulated random media were studied.The mathematical expression of auto-correlation function of diffusion light in an infinite medium modulated by ultrasound was obtained.The influences of ultrasound and scattering parameters on modulation parameter,modulation amplitude and its decaying were discussed.The feasibility of imaging an object hidden in random media with an auto-correlation function was also studied by use of Monte Carlo simulations.The ultrasound-modulated auto-correlation functions of normal and diseased tissues are different,which can be used to diagnosis diseased tissue hidden in normal tissue.