Abstract: A new swing laminography(SL) method is presented based on micro focus X ray imaging system to conduct non destructive testing on the slender shaped multi layer samples. Computer simulations are made to analyze the limited projections in SL and the principle of choosing optimal projection angular region(OPAR) in limited projection is discussed. The applied result shows SL with 120°swing angles distributed in OPAR can get the image of each layer in a two layer printed circuits board.