The invention discloses a reactor core of a molten salt reactor. The reactor core of the molten salt reactor comprises an active region and a reflecting layer, wherein the reflection layer covers theactive region; the active region is formed by fuel assemblies through array assembling; the volume of the active region molten salt passage accounts for 2 to 25 percent of the volume of the active region; the active region comprises a center region and an edge region; the volume ratio of the center region to the edge region is 1/15 to 1/8; the volume of the single molten salt passage of the centerregion accounts for 40 to 50 percent of the volume of the single molten salt passage of the edge region; the cut edge is the arc cut side edge. The molten salt passage of the reactor core of the molten slat reactor is positioned at the side edge position of the fuel assembly; the space self shielding effect regulation range is large; the deformation stress caused by radiation can be reduced; a narrow seam and the molten salt passage are communicated so that the reactor core molten salt can realize the transverse flow mixing; the heat transfer is facilitated; a dead region is avoided; the fastneutron radiation rate of graphite in the reactor core center region is reduced; the service life of the reactor core is prolonged; opening collecting structures at the two ends of the assembly can realize the flow rate distribution regulation; the fast neutron injection quantity of the upper and lower cavity alloy is reduced.