In this paper we propose the secure transmission for secondary user in cognitive radio network(CRN). Here the relay selection is used to protect the secondary transmitter(ST) and secondary destination (SD)against eavesdropper with the aid of both single and multi relay selection. In multi relay selection of secondary transmission are chosen for simultaneous forwarding from ST–SD. In the presence of eavesdropping ,on relaxing the intercept probability it is observed that outage probability of direct transmission and relay selection improves. This phenomenon is called security reliability trade-off(SRT).From our deduction ,using filter and forward relay we conclude that SRT of single and multi relay schemes are better than that of direct transmission and as the number of secondary relay increases the SRT of single and multi relay selection scheme improves therefore we can conclude that when using filter and forward relay transmission scheme performance of multi relay selection is found to be comparatively better than single relay selection scheme.