RF-TV overlay EPON technique is investaged. First, the interference problems between 1550 nm CATV path and 1490 nm data path are described and then the theoretic formula of the nonlinear crosstalk from 1490 nm to 1550 nm lightwave via stimulated Raman scattering effect in the optical fiber and the linear crosstalk from 1550 nm to 1490 nm lightwave caused by in-sufficient wavelength isolation of the CWDM coupler are presented, based on which the quantitative analyses and computation examples are given. The results show 9 dB carrier-noise-ratio degradation at the low end of CATV band due to the nonlinear crosstalk from data and 2.5 dB optical power penalty for data receiver due to the linear crosstalk from CATV in the case of conventional taper-fused CWDM. At last proposals to solve the crosstalk problems are offered including Ethernet idle scrambling, high isolation CWDM etc..