Aiming　at　the　defect　of　three-dimensional　data　pre-processing　of　traditional　partial　least　squares　(MPLS)　in　batch　process　online　monitoring,　a　improved　method　of　MPLS　is　researched　to　do　online　monitoring　and　fault　diagnosis.　In　the　data　pre-processing,　the　method　combines　the　advantages　of　traditional　expanding　methods.　It　contains　information　of　different　batches　that　remove　the　nonlinear　and　dynamic　characteristics　of　the　process　at　a　certain　extent,　as　well　as　resolving　the　problem　of　data　filled　in　online　applications;　In　calculating　the　monitoring　statistic　of　T-2,　the　method　researched　in　this　paper　uses　time-varying　covariance　to　replace　the　fixed　one　of　principal　components,　which　fully　considers　the　dynamic　characteristics　of　the　score　vector.　Meanwhile,　aiming　at　the　problem　of　characteristic　of　lagging　in　process　that　the　ordinary　contribution　plot　method　is　difficult　to　correctly　display　the　source　of　the　fault　of　the　current　moment,　a　fault　diagnosis　method　based　on　time-varying　contribution　plot　is　proposed　in　this　paper.　The　improved　method　was　proved　to　be　effective　by　comparing　with　traditional　MPLS　through　experiments.