Security is the most important aspect of any infrastructure. Infrastructure may be of private organization or government organization and the economy of the nation depends on this infrastructure. A no. of approaches have been developed and proposed of researcher to ensure the security of critical infrastructure. This paper surveys the existing techniques for critical infrastructure protection. SCADA is defined as Supervisory Control and Data Acquisition. SCADA is considering as critical infrastructure. This paper also provides some important techniques for protection of SCADA.