This paper proposes a design of CubeSat communication system between ships and ground station for Automatic Identification System (AIS) using Software Defined Radio (SDR). The CubeSat operates as a relay point to increase the ground station’s detection range. The communication system design is divided into three subsystems; AIS, data communication, and Telemetry, Tracking & Control (TT&C). Each subsystem utilizes Very High Frequency (VHF), S-band and Ultra High Frequency (UHF) respectively. Data communication uses Differential Phase Shift Keying (DPSK), while AIS and TT&C use Gaussian Minimum Shift Keying (GMSK). The simulation takes into account Doppler shift in space communication. Based on the result from link budget analysis, the communication system satisfies the design specifications. This indicates that the proposed CubeSat communication system is applicable for AIS.