Abstract: A new Open Service signal adopting CBOC modulation is introduced in GNSS. Due to the multi-peak in the auto-correlation function envelope of CBOC signal, the acquisition is made more complex. In this paper, a fast unambiguous acquisition method based on FFT is presented to acquire CBOC signal. The proposed method utilizes two orthotropic local sub carriers to eliminate the ambiguity introduced by the multimodality of the ACF envelop, and also adopts an FFT-based acquisition structure to significantly reduce the time expenditure on acquisition procedure. Moreover, three receiver modes, i.e., BOC(1,1) reference receiver, Non-coherent CBOC reference receiver and Coherent CBOC reference receiver, for the proposed method are presented and analyzed. Performance of the three receiver modes are also analyzed and compared. Results of Monte Carlo simulations show that the proposed method can acquire the CBOC signal quickly and correctly, and is superior to the BPSK-like method. Besides, Coherent CBOC reference receiver owns the best performance in the three receiver modes.