Abstract: A novel space-time adaptive processor based on variable diagonal loading is proposed. On the basis of analysis of constraint equations, the actual space-time steering vectors of the desired signal can be solved using the Lagrange multiplier methodology. The optimum weight vector of space-time beamforming algorithm can be calculated. And the amount of diagonal loading can be precisely calculated based on the uncertainty set of the space-time steering vectors. Results of computer simulation verify the efficiency of the proposed algorithm.