Abstract: Fake block attack intends to prolong the downloading time by providing fake data to make the file block fail in the hash check. P2P file-sharing systems are susceptible to fake block attacks, whereby malicious clients are able to make a big impact on users’ downloading experience. An efficient methodology named Smart-blacklisting, which aims to lessen the downloading time and bandwidth wastes interfered by the attack was proposed through using a mathematic model, and the efficiency of this method was analyzed during a simulation experiment. The ovel approach presents 87% downloading time and 50% bandwidth wastes compare less than those of eMule blacklisting method.