The predistortion linearization technique is usually used to suppress the composite triple beat distortion (CTB) in optical fiber amplitude modulated cable television (AM CATV) externally modulated transmitters. The influence of the incident polarization state with TE mode and TM mode on the CTB performance in optical fiber AM CATV externally modulated transmitters is analyzed with calculation and experiment. The theoretical analysis and calculation have shown that the TE mode is the best mode for performance of CTB suppression. The influence of the incident polarization state drifting off TE mode is also analyzed and measured, and it is shown that the deviation angle from the TE mode should be less than 15 degree so as to the performance for CTB suppression will not be degraded.