Abstract: The network can be a hotbed of rumors, but also can be a powerful tool for dispelling rumors. Either treating internet as the chief cause of rumor or a sharp weapon for rumor self-purification is a poor description of internet's influences on rumor, which essentially, is "Media Determinism". According to a investigation report by the research institute of People Net: various types of rumor do not have the same ability of self-purification online. Rumor about science can purify itself very well, while people discussing rumors about the rich, the police and government officials online tend to hold extreme views; rumor involving public security could be"controllable rumor",and whether it can get self-purified relies heavily on numerous external conditions. Analysis of several"controllable rumors"reveals that if the vulnerability of a rumor can be sensed right after its spreading, and furthermore, if the government can offer authoritative information, after which the media, opinion leaders and the party provide diversified sources of information, the function of internet's self-purification can get started, and the ability of internet's self-purification can be turned into reality.