Introduction  As an important energy-saving equipment in reverse osmosis seawater desalination system， the system design of energy recovery unit is very important.

  Method  In this paper， from the aspects of design principle， working principle， design calculation， equipment configuration and selection， the three most commonly used energy recovery unit system designs were compared in detail.

  Result  After the system design comparison， the advantages and disadvantages of the three energy recovery units are obtained for designers to choose.

  Conclusion  This paper provides designers with targeted and effective design guidance and improves design efficiency.