Domination of Cloud computing in IT field will influence enterprise informatization style deeply to provide an alternation of infrastructure construction of informatization by renting hardware services from SaaS providers. However, not all enterprises are suit for SaaS services. Only proper construction style based on their realities may low investment risks, cut costs, and improve core competition of enterprises. Three styles of infrastructure construction of informatization are concluded in this paper, and the core is how to compare costs among them. With the help of CloudAnalyst, detail cost of infrastructure construction of informatization could be simulated, which could provide scientific suggestions for enterprise managers.