Abstract: In this paper,the origins of the physical effect of microgra-vity that occu in fluids are described and the physical effect of microgra-vity is divided into two kinds—the first grade effect and the second gradeeffect by the mentioned ideas.We have made a relationship between spaceprocessing of various materials and the second grade physical effect ofmicrogravity,and also made and estimation for the microgravity level,onwhich various physical effect of microgravity would occur,respectively.