To evaluating and measure the security of an enterprise or a public network is an important step for the security of network itself and defence outside threat. So many of the current research in cyber analysis were focusing on it. In the field of network security, others have used CVSS, security metrics and attack graph to evaluate software systems or automation systems. However, no article has used these methods to study the SME(small and medium-sized enterprises) network, and there is no complete set of methods to evaluate the topology of the SME network, as well as which security metrics to use to evaluate the network and which metrics are the most important, there is no conclusion at present. Therefore, this paper will use the research results mentioned above to focus on solving this problem. In this paper, first of all, we tried different network constructing technique, and used attack graph to generate the absorbing Markov chain model, then calculated the security metrics base on CVSS. Finally, we analyzed the meaning of different metrics and the score of each of them and gave the suggestion for improvement for this network. Finally, we found that when faced with the network topology of small and medium-sized enterprises, the various metrics are only relatively important, and there are no completely unimportant metrics. Therefore, security engineers need to model the topology structure of the network and use tools to generate the attack graph, calculate the security metrics and make adjustments when building the network. Security engineers need to comprehensively consider various metrics to adjust and analyse the network to determine the security of the network, instead of adjusting the network after it's built.