Abstract: A law for 3-dimensional wing is provided on the basis of a matrix method.Formula（1）is its basic equation,and the definition of the equivalent angle of attack αv is given by formula（7）.[A]denotes the vortex introduced matrix and [AT]——the reverse-flow introduced matrix.The equivalent angle ofattack for the whole wing with linear camber-twist can be given by equations（23）,（24）,（25）,（26）,where X0,Z0 are coordinates of the aerodynamic center in reverse flow.The above conclusion is capable of substitution for the two-dimensional Pistolesi theorem.