We research on cooperative information security transmitting using energy harvest amplify-and-forward relay in the wireless information and power transfer network with multiple eavesdroppers. Two low-complexity methods using zero-space beaforming technique are proposed. Using the prior location information of receiver or eavesdroppers

our methods project the target vector to the zero space of receiver or eavesdroppers. Computational complexity of the method is lower than that of classical method since space freedom of the target vector is reduced. Furthermore

second method induces the eavesdropper's mutual information of objective function to be zero

the original quasi-convex problem is transformed into a convex form. Thus

computational complexity of the method is apparently reduced compared with that of classical method. Result of experiment verify validity of our proposed methods.