Abstract: By use of non-crimp fabric(NCF), CYCOM^® 890 RTM and PMI foam, the influence of pumping on sandwich panel interface quality and fiber volume fraction in VARI process were studied in this article, the types and causes of defects by the means of mechanical properties testing and microstructure analysis of the composite sandwich plate were analyzed and the process parameters were optimized. The results show that the pumping step is conducive to improve fiber volume fraction and mechanical properties for the composite sandwich structure. Pumping from 100 ℃ to 120 ℃ within 30 min in a stable technology, the interlaminar shear strength and flexural strength increase significantly.