To improve the throughput and decrease the suffered interference of TDCS, the double-threshold energy detection is proposed to estimate the spectrum environment around TDCS. By comparing the detected spectrum value with the double thresholds, the spectrum with the statistic above the upper threshold is marked as 0, and below the lower threshold is marked as 1, while that between the double thresholds is marked as 0.5. The basic function at time domain is obtained by operating IDFT to the product of spectrum marker and pseudo random phase. TDCS implements communication by modulating data on the basic function with CCSK. Simulation shows that compared with the traditional single-threshold TDCS, the proposed double-threshold TDCS bears lower BER and higher throughput.