Abstract: The relationship between the plane shape of foundation pit and its stability is found in foundation pit observation practice. It furnishes observation data of stress and displacement of ellipse foundation pit, round foundation pit and rectangle foundation pit. The superiority of ellipse foundation pit and round foundation pit is pointed out, based on site observations. It reaches the conclusion that the ellipse or round foundation pit advantageous than the rectangle foundation pit. The load-bearing capacity and pit wall stability of ellipse or round or rectangle foundation pit are analyzed by three-dimensional finite difference integral method. The ways and process of foundation pit observation are given.