The invention discloses an automatic enveloping, jar mounting and welding device and a method thereof. The device comprises a welding wire, a battery jar output conveyor, a jar mounting and enveloping auxiliary mechanism, a rotary plate mechanism and a battery jar mounting mechanism, wherein the rotary plate mechanism and the jar mounting and enveloping auxiliary mechanism are mounted in a matching manner; a horizontal motor is mounted on a mechanical hand bracket; a vertical motor is mounted at the lower part of the horizontal motor; a clamp is mounted at the lower part of the vertical motor; a plurality of enveloping tanks are mounted on a cluster conveyor belt; the battery jar output conveyor is mounted at the lower part of the rotary plate mechanism; one end of the battery jar output conveyor and the welding wire are mounted in a matching manner. The method comprises the following processes: cluster enveloping, cluster mounting clamps, cluster arrangement and clamping, conveying plastic battery jars, cluster mounting the battery jars, outputting the battery jars, flame welding and conversion operations of the batteries after welding. According to the automatic enveloping, jar mounting and welding device, the degree of automation of the device can be improved, the processes are arranged in a more reasonable manner and the production efficiency can be improved.