Abstract: Aiming at the deficiency that unable to provide effective security information about network data transmission information in current LAN security evaluation system, a security evaluation method, which analyzes the self-similarity of traffic on router, is proposed.After choose the suitable time-scale, whittle estimator is applied for calculate the self-similar parameters of four evaluate metrics.We study the abnormal situation of traffic on LAN by calculate the distances between the self-similar parameters and normal values.A reformative model for evaluates the LAN's security is given on the base of before-mentioned method.Experiment results show that our method is able to evaluate the abnormal change on traffic caused by several reasons.It provide system administrator with intuitive security curve that expresses the risk of network system data transmission.