In Orthogonal Frequency Division Multiple Access Passive Optical Network (OFDMAPON) upstream transmission,the Optical Beating Interference (OBI) will be produced if each ONU uses different lasers with the same wavelength.The colorless ONU is hard to achieve with the presence of OBI.The OFDMAPON system structure was studied and the related formulas were derived to analyze the generation and avoidance of OBI.The OBI avoidance scheme that sending optical carrier used in upstream by downstream transmission combined with coherent detection in optical line terminal was simulated.Via simulation,the antidispersion scheme and the effects of dispersion accumulation and the length of training sequence on system performance were studied,and the parameter configuration was optimized to provide a theory reference for practical application.