Abstract: Lead-based fast reactor (LFR) is one of the most promising types among the Gen Ⅳ nuclear reactors. It has better transmutation and breeding capability, as well as higher passive safety and economical efficiency, and it is easy to be miniaturized. As a result, LFR becomes a major concern in the nuclear industry. In this paper, the main concepts of LFR were concluded. A research tendency on small modular LFR was indicated and the existing challenges were pointed out. There are mainly 5 key thermal hydraulic issues of LFR, namely the flow dynamics and heat transfer of the coolant, thermal-hydraulic phenomena in reactor core and lead pool, system safety characteristics and some specific thermal-hydraulic phenomena of LFR. The research progress in these 5 issues was analyzed and the current research findings were concluded. Besides, the research tendency and difficulties in each research direction were suggested. This paper can provide useful information for LFR design and thermal-hydraulic analysis.