Volunteers play a vital role in the service and support of American libraries. Through an investigation of 152 American urban libraries in the authoritative American Urban Library Committee (UCC), this research explores the current model of volunteer services and their characteristics. The results indicate that rules and regulation information for volunteers to work in the US urban library is easy to obtain, public policy is openness, application methods can be divided into three categories, and the recruitment process is also coherent across these libraries. The research also finds that the libraries tend to hire younger volunteers, and most of them have little or no requirements for skills and work experience, furthermore, the working hours can be negotiated. Although the American Urban Libraries have formed a standardized and systematic volunteer service model, they still face many practical challenges that need to be solved. Hopefully, these findings and analysis can be exploited in future works as a useful source of information to guide volunteer services in libraries in China.