Theoretical analysis of "the characteristics of gravity work" is more abstract, and the students'' understanding of "gravity work has nothing to do with the path, and the height difference of the position of the object is not comprehensive enough". Based on the analysis of high school physics textbooks, this paper makes a gravity work inquiry instrument by using easy to get materials in life. Through experiments, it intuitively presents the characteristics of "gravity work has nothing to do with the path". Practice has proved that the instrument is simple to make, obvious phenomenon, convenient to operate, easy to promote and use.