Abstract: Aiming at the problem that it is difficult to estimate the combination code sequence of Alternate Binary Offset Carrier (AltBOC) signal, an improved k-means algorithm is proposed for blind estimation of AltBOC signal combination code. The method firstly constructs the AltBOC signal model by introducing intermodulation component and rebuilding the subcarrier. Then, the AltBOC signal was segmented into a non-overlapping observation date matrix with period window length of combination code at the receiving end, and the optimal sample was selected from the observation data as the initial mean vector in K-means clustering by using the similarity principle. Finally, the square error of the date sample and its clustering mean vector was iterative optimized by the K-means algorithm to complete the blind estimation of the AltBOC signal combination code sequence. Computer simulation results show that the proposed algorithm can accurately estimate AltBOC signal combination code sequence at SNR -15dB.