In order to study the practical applicabality of the 3rd-order distributed Raman amplifier (DRA) in Cable Antenna Television (CATV) system, the structure of the 3rd-order DRA is put forward firstly, and the effect of higher order simulated Raman scattering is investigated. Moreover a simulated 3rdorder DRA-CATV system over 120 km fiber is set up to study its performance of 16-QAM as the main digital signal. In order to compare the performances, a simulated 1st-order DRA-CATV system is also set up. Simulation results indicate that the bit error rate (BER) of 16-QAM in the 3rd-order DRACATV system is lower than that in the 1st-order DRA-CATV system. The theory results are beneficial to apply a higher-order Raman pumping (HOP) DRA for the future experiment.