This article mainly introduces the principles and implementation of the WAND (Weak AND) algorithm. WAND is a search algorithm applied in scenarios where a query has multiple keywords or tags, and each document also has multiple keywords or tags (such as search engines). Especially when the query contains many keywords or tags, WAND can quickly select the Top n relevant documents. The original paper of the algorithm can be found at Efficient Query Evaluation using a Two-Level Retrieval Process. This article mainly explains the principles of this algorithm and implements it in Python.