The coherency problem affects greatly the reliability and quality of concurrent object-oriented software. Hence, Java provides the "synchronized" mechanism to help user to deal with coherency problem in multithreaded object-oriented programming. However, improper use of the "synchronized" mechanism will result in system deadlock, which also violates the requirement of software reliability and quality. In the paper, we set up a new description tool named Thread Diagram. Based on Thread Diagram, we propose a new approach to analyze potential deadlock in Java multithreaded programs with "synchronized" mechanism.