To solve the problem of blind estimation of spread spectrum sequence period for multi-carrier code division  multiple access (MC-CDMA) signals in multipath fading channels, two algorithms, secondorder moment of autocorrelation and cyclic autocorrelation, are proposed. By analyzing the second moment of autocorrelation for the MC-CDMA signal under the multipath fading channel condition, the spread sequence period for the MC-CDMA signal is estimated. By analyzing the cyclic autocorrelation of MC-CDMA signals under the multipath fading condition, the period of spread sequence of MC-CDMA signals is estimated. Finally, the two algorithms are simulated respectively under different channel conditions, and the performance of the two algorithms is compared and analyzed. Theoretical and simulation results show that the cyclic autocorrelation algorithm has good performance in estimating the spread spectrum sequence period for MC-CDMA signals at a low signal-to-noise ratio, but the second-order moment of autocorrelation algorithm has lower computational complexity than the cyclic autocorrelation algorithm, and this algorithm is easy to implement.