The compensation of Composite Second Order Intermodulation (CSO) caused by Self Phase Modulation (SPM) and chromatic dispersion in 1550nm long distance fiber CATV systems were discussed.The CSO formula in the long fiber link with casecaded EDFA′s was obtained,and then modified in the case of using chirped fiber grating for dispersion compensation.The analysis and experiment demonstrate that the effect of dispersion compensation is sensitive to the compensator position.The optimal position can be deduced through a theoretical model and verified by simulation and test.