Laser frequency offset and phase noise are important factors that limit the Coherent Optical Orthogonal Frequency Division Multiplexing（CO-OFDM）system performances.This paper proposes a novel scheme based on differential pre-coding and Multi-Carrier Differential Detection（MCDD）algorithm

which can jointly compensate the laser phase noise and frequency offset

theoretically derives the principle of the frequency offset and laser phase noise in CO-OFDM systems and the working mechanism of the MCDD-based compensation scheme

and conducts system simulations in different OSNRs

laser frequency offsets and linewidths.The simulation results indicate that this scheme has good compensation effects and large compensation scope and effectively improves the CO-OFDM system performances even without introducing extra system overhead.