The Japan Atomic Energy Agency (JAEA) has been promoting research and development on the hydrogen production technology with a high-temperature gas-cooled reactor (HTGR), with a view to contributing to the global warming issue and hydrogen energy society in the near future. The system integration technology for connection of the hydrogen production system to the HTGR is one of the key technologies to put hydrogen production with nuclear energy to commercial use. Research and development on the system integration technology has been carried out for four items: control technology to maintain reactor operation against thermal disturbance caused by the hydrogen production system, estimation of the tritium permeation into the hydrogen from the reactor, a countermeasure against explosion, and development of a high-temperature valve to isolate the reactor and hydrogen production systems in accidents. This report describes the research activities on the system integration technology at JAEA.