Online advertisement (short as ad) has become one of the most important business patterns, with the rapid development of Internet. Online advertisements are main economic sources of Web applications, but the negative affect is that ads may leak users' privacy, or increase loads of browsers' performance. In order to study online ads systematically, it is necessary to obtain a complete call path in the whole generating process. However, since the sizes of the loaded JavaScript files are usually large, the function call path is long, and even worse, the JavaScript code in the path is compressed and confused, it is difficult to get the call path of the online ads through static analysis method. This study tracks the call path of online ads dynamically, namely instruments the relevant codes at first, then uses the function parameters to transmit the call information and records the internal call information in each iframe, finally, by matching and merging the information in multiple iframes, a complete ad call path about the generating process of online ads is generated. The experiment focused on 21 real websites, and the results show that:the proposed method can obtain the dynamic loading information of ads and generate the whole call paths, which are impossible for static methods, and the overhead is acceptable.