Cognitive radio is the most effective technology to solve spectrum scarcity problem in contrast to high speed data transfer need. In cognitive radio systems, non-licensed users are permitted to use a licensed user spectum bandwidth whenever is not used. As soon as the license holder begin to use its spectrum, non-licensed user stops its communication and waits untill the licensed user finish its communication. The most important parameter in cognitive radio systems is reliable detecting the idle or busy status of the spectrum. There are many types of spectrum sensing methods but covariance based spectrum sensing, there is no need for any information about the environment and licensed user signal which eliminates the error could cause by these factors. In this paper the concept of double threshold is used for the best known covariance based spectrum sensing which is maximum to minimum Eigen-value based method and double threshold maximum to minimum Eigen-value method is introduced.