Process quality ultimately decides on the quality of electronic products. Based on analyzing and improving process capability index (PCI), microelectronics process quality of electronic products may be effectively assured. Nowadays with the rapid development in microelectronics process, Quality evaluation of processes concerns more than one quality characteristics, microelectronics process quality evaluation concerns multi quality characteristics, therefore univariate PCI is difficultly used to synthetically analyze microelectronics process quality. The paper presents a multivariate PCI based on weight factor, which provides references for assuring and improving process quality while achieving overall evaluation of process quality and is not limited to the variable number. An example of calculating multivariate PCI (MPCI) is given. Real application shows that the method presented is effective and actual.