This disclosure provides a computer-implemented method for monitoring an application at runtime. The method comprises building up a calling relationship graph for at least one type of system method called at runtime, by checking a stack trace generated when the application is running. An application method of the application that directly or indirectly calls this type of system method is represented as a node in the calling relationship graph. The method further comprises determining one or more target nodes in the calling relationship graph by analyzing the structure of the calling relationship graph. The method further comprises inserting callback methods into application method(s) of the application corresponding to the one or more target nodes only in a calling side. The method further comprises monitoring the application at runtime by using said callback methods.