Aiming at the problemthat there is no calculation formula about the yield of rhombic inverted nine-spot areal well pattern in lowpermeability reservoirs up to now, based on the water flooding theory of lowpermeability reservoirs, the yield formula for calculating the rhombic inverted nine-spot areal well pattern was deduced by using the basic formula of low rate non-Darcy flow, flow line integral method and element analysis method. The application range is wider than the square inverted nine-spot areal well pattern. The production rate of eight wells of low permeability reservoirs in the BYS block of Ordos Basin was calculated by the method. The result is close to the real yield, with a relative error of only 8%. Adaptability of the rhombic inverted nine-spot areal well pattern in BYS block was evaluated by using the startup coefficient. Aremarkable result has been obtained preliminarily by the optimization and adjustment in BYS block.