Aimed at the problem that TDMA,FDMA and CDMA do not adapt to cognitive radio(CR) for its non-continuous,random and variable spectrum,a system about multiple access of CR based on transform domain communication system(TDCS) is proposed.It avoids disturbing the primary users through making the amplitude of busy spectrum be zero.The m state sequences are adopted to produce random phase vectors.Basis functions on modulation produced by phase vectors are orthogonal and can achieve multiple access.Data are estimated through making the correlation of the signal and basis functions of receiver,and the theoretical BER of this system is analyzed.Simulations show that the detection probability,the number of accessed users and the difference of basis functions between the transmitter and receiver will affect the performance of this system.This system can use the non-continuous spectrum,and its basis functions are self-adaptive,which make it be used in CR.