This document presents a secure and efficient scheme for multi-keyword ranked search over encrypted cloud data that supports dynamic operations like document deletion and insertion. It constructs an index tree based on the vector space model to enable multi-keyword search while supporting flexible updates. Cosine similarity is used to accurately rank search results. The scheme also proposes a "Greedy Depth first Traverse Strategy" search algorithm and a secure scheme to protect search privacy in the known ciphertext threat model.