Abstract: To deal with the disadvantage of large computational load for derivative based updating(DBU),a method named reduced dimensional DBU algorithm is proposed.The algorithm uses the matrix blocking reverse theorem to get a revised matrix,then uses the reduced dimensional space time adaptive processing(STAP)method of 3DT.This method can decrease the computational load and reduce the number of independent identically distributed(IID) samples,and it approximates to the original optimal DBU method in performance.The results of experiment show that the method can still obtain a good performance near the optimal processing under clutters with some uncertain errors.