API (application programming interface) is widely used in modern software development process. Developers save a lot of time when they quickly build projects through invoking APIs. However, API is often difficult to use for many reasons, such as the presence of large number of interfaces, lack of perfect document, and no timely maintenance and updates. Further, API is often used incorrectly, resulting in bugs and sometimes significant security problems.This paper summarizes the recent domestic and overseas research results based on a thorough survey of the API related literatures. Firstly, it introduces the API concept and recognizes the three key issues that affect the API usage:poor API documentation, incomplete invocation specification and undetermined API call sequence. Next, it analyzes the latest advances from these three main aspects:API document, invocation specification and API recommendation. Finally, this paper outlines the challenges of the future research.