Abstract: The characteristics of route protocol and access control in computer network make the topology have some phenomena such as single-direction and asymmetry. For these reasons, some links can not to be found during the topology discovery. In order to resolve this issue, a bidirectional topology discovery protocol (BTDP) is proposed, which is based on measurer spreading and sub/pub mechanism. The measurers who want to make use of this protocol can probe for other's links which can not be discovered by oneself from destination to source. An automaton model of this protocol is created. Analyzing and validating the model prove that the protocol's computability can be end in logic. Further we give the algorithms for the protocol, including the main part which finishes the process between source and destination, and the fusion part which is to judge the links whether they are the same and to fuse them. Finally the algorithm is implemented with program. Through the plus of QQ instant communication software, a group can be deployed to implement the topology discovery. The experiment in which program is running on the Internet of China show that BTDP can find the asymmetrical paths in this network. On the other hand, the fusion data coming from multi-measurers reveal some hide-links in the above environment.