Abstract: In a sidelobe cancellation system， the desired signal can also be eliminated when the number of auxiliary antennas is larger than the number of interference sources. Generally， this problem can be solved by adding a blocking matrix on the auxiliary channel. However， the sidelobe shows great uplift when the direction of the desired signal is closing on the that of the interference signal. To address the issue， a novel method is proposed in this paper， which eliminates the desired signal from the auxiliary antenna by adding a linear constraint on its output. It is observed through simulation that the new method maintains the max gain in the direction of the desired signal while forming an optimal null in the direction of interference.