Subspace obtained by SVD is fit for complex interference and few sample, but computation of this method is large. A new subspace projection approach was proposed. It relaxed the requirement of the diagonal matrix in SVD to block lower triangular matrix and reduced the computation while the anti-jammer performance was not affected. The block lower triangular matrix can be computed by Givens rotation. Givens rotation has modular structures and is suitable for parallel computation. Based on the characters of GNSS signal, noise and jammers, it is applied to interference suppression in GNSS receiver. The numerical simulation demonstrates that the performance is effective.