Cognitive radio (CR) is studied as a important technology in the next-generation network to resolve range shortage, by allowing effective use of the certified users' empty spectrum. (CRN) Cognitive radio network cooperative spectrum sensing provides a promising performance than the individual sensing method. Nevertheless, the presence of the malicious users' attack significantly degrades the output of cognitive radio networks by submitting inaccurate data to the fusion centre. Adaptive threshold technique based on trust value algorithm is proposed to differentiate the malicious user and the doubtful user from the legitimate user by initially assigning the trust values to all the users. Adaptive threshold mechanism is used here to provide a reasonable circumstance to the hesitant customers to verify their integrity. A untrustworthy client is said to be a malicious user when it fails the adaptive threshold test. At the fusion center, the output of the legal users are merged.