An assembly structure for assembling a first plastic shell and a second plastic shell, thereby coupling articles to be assembled such as keyboards and adapters, including a hollow strut and an opening. The first plastic shell has the hollow strut extended from the inner side. The second plastic shell has the opening defined therein and corresponding to the hollow strut and extends inwards to form an annular flange abutting the hollow strut. The hollow strut has a portion extended through the annular flange to be melted by the ultrasonic welding technique, the thermal welding technique, or the combination thereof until reaching the annular flange, to couple the first and second plastic shells for facilitating assembly. Grinding off the melted portion may disassemble the first and second plastic shells. The disassembled the first and second plastic shells may be coupled again by fastening a fastening element in the hollow strut with the head of the fastening element held by the annular flange.