The invention provides an automatic continuous cast welding method for lead-acid batteries and a cast welding machine thereof. According to the method, firstly battery clamps from the previous procedure on the conveying line are pushed in order in a feeding position, the battery clamps reach a cast welding position where the battery clamps undergo die-closing operation, cast welding operation anddemoulding operation in sequence at the same time, then the battery clamps are delivered to a loading position for loading to separate pole plates from batteries and put into boxes, the batteries arepushed to the next procedure after separation, and the empty battery clamps return to the previous procedure for continuous recycling. The feeding position, the cast welding position and the loading position are arranged linearly in sequence. During cast welding, a plurality of cast welding mechanisms of the cast welding position alternately perform cast welding operation on a plurality of groupsof batteries at the same time, and the feeding operation, the cast welding operation and the loading operation are completed independently and continuously. With the scheme, the time is saved, the machine is simple and compact in arrangement, the size of the cast welding machine is reduced by more than 3/4 compared with the prior art, the cost is reduced, and the output of one production line canbe achieved by using one lead smelting furnace.