The invention discloses a chain inner link fast assembly mechanism. The chain inner link fast assembly mechanism comprises an upper die seat and a lower die seat which are in up-down parallel and are arranged horizontally. A telescopic guide rod is arranged between the upper die seat and a lower die seat. The lower die seat is provided with a plurality of support shafts, and sleeves to be assembled with inner links penetrate through the support shafts. A round boss fixed to the lower die seat is arranged on the lower portion of each support shaft. The round bosses are arranged around the lower portions of the support shafts. The upper die seat is provided with a plurality of through holes through which the support shafts penetrate. The through holes penetrate through the upper die seat. The multiple through holes are in un-down one-to-one correspondence with the multiple support shafts. The part, located over the space between every two adjacent support shafts, of an upper die seat body is provided with a protruded extrusion bosses. According to the chain inner link fast assembly mechanism, the assembly process is fast and convenient, the assembly precision is high, the assembly forming effect is good, the overall structure is simple, installation and operation are convenient, the manufacturing cost is low, the assembly efficiency is improved, and the practicability is high.