Abstract: With focus on blind estimation of the PN(Pseudo-Noise) codes for periodic long-code Direct Sequence Spread Spectrum(DSSS) signals with residual carrier after down-conversion, a blind estimation approach of PN codes is proposed based on Eigenvalue Decomposition and Digital Phase Locked Loop(DPLL). The chip rate of the PN code and the PN codes period need to be known. Firstly, the periodic long code DSSS signal with residual carrier is equivalently modeled as a virtual multiuser short code DSSS signal model. The PN codes with residual carrier can be estimated by the matrix eigenvalue decomposition and fuzzy unitary matrix methods. Then, a DPLL is used to track and estimate the frequency and phase of the residual carrier, and remove the carrier frequency in the end. Finally, the PN codes can be estimated by removing its segmentation phase ambiguity with the condition of the specific constraint(such as m sequence and Gold sequence). Theoretical analysis and simulation show that the proposed approach can work effectively under low SNR and exhibits good performance