Network coding provides a new perspective for anonymous communication. Wang et al. propose an anonymous communication scheme named ALNCode, in which the linear relation of the global encoding vectors can be hidden without the participation of encryption/ decryption operations. But the effectiveness of the scheme needs to be further analyzed. In this paper, we present an exact formula of the effectiveness of ALNCode scheme, which goes a step further than the lower bound given by Wang et al.. Based on the exact formula, the influential factors of effectiveness of the scheme are taken into account in details. Moreover, a comparison between the exact effectiveness and the lower bound shows that the lower bound is not true. The reason of the error is analyzed finally.