The invention relates to an automatic positioning mechanism for a movable heavy-load pallet. A tensioning electric pull rod support and a rotary pull rod support are respectively arranged on a positioning base, a rotary guide sleeve is arranged on the rotary pull rod support, a rotary pull rod penetrates through the rotary guide sleeve, one end of the rotary pull rod is connected with a tensioningelectric pull rod which is arranged on the tensioning electric pull rod support through a connecting shaft, the other end of the rotary pull rod is connected with a tensioning claw, and a buffer mechanism for buffering the movable heavy-load pallet is installed on the rotary pull rod support; and the two sides of the positioning base are connected with limiting guide mechanisms respectively, anda plurality of universal limiting modules are uniformly distributed on the limiting guide mechanism on each side of the positioning base in the length direction. The automatic positioning mechanism for the movable heavy-load pallet automatically adjusts and pulls the moving direction of the movable heavy-load pallet, automatically buffers and absorbs large kinetic energy cause by large impulse caused by large mass, and achieves the positioning work of a plurality of varieties of large-mass movable heavy-load pallets with strict requirements on positioning precision, thus having prominent characteristics, high positioning precision and reliable work effects.