In this paper, by using effective leakage value, we quantitatively assess the security performance of the fiber-optic wiretap channel with forward error correction coding. As the eavesdropper is far from the transmitter, effective leakage value initially decreases slowly and then will vary rapidly. As the eavesdropper is close to the transmitter, effective leakage value of (7,4) block code is larger than that of the (7,3) block code. However, when the eavesdropping distance is far, the system security performances of both are almost the same. Furthermore, effective leakage value using OTDR is analyzed and discussed.