In this work, a spectrally efficient 6-user APDCDM based Optical communication system is theoretically investigated and verified using simulation. The data rate considered here is 10 Gbps for each user and it propagates over 150 km standard single mode fiber. Average energy per bit with and without guard band is calculated for all the 64 cases of 6×10 Gbps system. Performance parameters like BER, receiver sensitivity and null to null bandwidth is also evaluated for this system. The simulation design and the analysis are performed using Optisystem and MATLAB.