Design and calculations of buttress of pressure pipes elbow curved downward are introduced in a variety of documents． It can be checked in the standard atlas and obtain the size of the buttress directly． However，the standard atlas has the following features: The atlas takes up a large space and the range of parameters is limited． When the actual parameters are outside the scope of the atlas the butt size can not be found． When the actual parameters are not equal to the parameters in the standard atlas，only the approximate value of the buttress size can be obtained and the error is large． The shape of the pier is not reasonable． Only the average base stress is checked without the unevenness of the base stress． But the former is not required to check and the latter is the key． No anti－overturn stability of the buttress is checked and there is no pier positioning size． This paper introduces the design and calculations of buttress of pressure pipes elbow curved downward． It overcomes the defects above and can directly solve the equation without a trial． The method in this paper is comprehensive，reasonable and simple．