Aimed at the problem that the decision threshold is difficult to precisely set and the complexity of hard decision is high, a new method of power spectrum flip to generate basis function is proposed based on the sampling and estimates of electromagnetic environmental and the environmental spectrum flip is used to construct basis function's amplitude spectrum. In this way, lots of the threshold setting and decision steps are eliminated, thus greatly reducing the computational complexity in the communication system. Furthermore, compared with the traditional ‘0’ and ‘1’ hard decision method, the new method can be used to generate the basis function with more frequency components and a better correlation performance because the jammed band is not discarded completely. Simulation results show that the new method of generating basis function in power spectrum flip can reduce the computational complexity of the communication system and simultaneously improve the correlation performance of the basis function, which provides a new way of thinking for the in-depth study of TDCS.