In this paper, the allocation approaches of auxiliary antenna based on the independent array elements、sub-array region and array element combination are designed for studying the impact of allocation of auxiliary antenna on performance of adaptive sidelobe canceller in air-borne phased array radar. The results showed that the performances of the cancellers are good and there are no obvious differences for most of proposed allocation approaches. The performance of canceller seriously deteriorate when the auxiliary antenna are allocated in the same a row or a column. The auxiliary antenna based on the single array elements have better interference suppression effectiveness than that based on multiple array element combination. Thus, this paper suggested that the auxiliary antenna can not be allocated in a row or a column and are constructed using single array elements as many as possible.