The utility model relates to an automatic clamp opening device of a stacking trolley of a casting machine. The automatic clamp opening device is characterized in that a relay is arranged between an I 10.5 on a 1794 IM 8 module of a PLC (Programmable Logic Controller) signal control clamp and a power supply. On end of the relay is connected with a 12V safety power supply, the other end of the relay is connected with a stacking rack of the casting machine through a lead, the other end of the 12V safety power supply is connected with a steel wire, and the steel wire and the lead for connecting the stacking rack of the casting machine are connected through a switch to form a loop. The automatic clamp opening device prevents the clamp and aluminum ingots on a finished product conveyor from extruding and damaging equipment and ensures safe and stable production running.