To solve the complexity problem in the design of radar signals with low probability of interception, this paper proposes a novel compound modulation signal, namely the Costas/CTPC compound signal of inter-pulse Costas frequency coding and intra-pulse chaotic two-phase code (CTPC). The introduction of CTPC increases the randomness of the signal phase. The composition of the composite modulation signal is analyzed theoretically. After parameter optimization, the autocorrelation function, cross-correlation function, power spectral density, and ambiguity function of Costas/CTPC signal are analyzed through simulation. The simulation results show that this signal has better autocorrelation performance than Costas, Costas/Bark, LFM/Bark, and Costas/LFM signals. It also has good anti-jamming and low-interception performances. Therefore, it is very suitable for radar systems with low-interception probability.