The invention provides a novel heat exchanger core. The novel heat exchanger core comprises a cover plate, a first heat exchange plate set, a second heat exchange plate set, ..., and a nth heat exchange plate set. The heat exchange plate sets are stacked, the cover plate is stacked on the outer side of the heat exchange plate sets, and each heat exchange plate set comprises more than one same heat exchange plate; each heat exchange plate is composed of a base body and a heat exchange flow passage processed in the base body in a chemical-etching mode, and the projection of flow inlets and flow outlets of different heat exchange plate sets in the direction perpendicular to the heat exchange plates is not overlapped with each other; each heat exchange flow passage is composed of straight flow passage bodies and oval flow passage bodies which are alternately arranged; the straight flow passage bodies are communicated with the oval flow passage bodies; the long axes of the oval flow passage bodies and the center axes of the straight flow passage bodies in the liquid flowing direction are located on the same straight lines; n is a positive integer larger than or equal to three. According to the novel heat exchanger core, the narrowing and widening flow passages are adopted, the flow passages are prevented from being blocked, and the novel heat exchanger core is particularly suitable for the working procedure of cooling natural gas on a sea working platform.