A head stack assembly includes a mounting base, a plurality of drive arms connected with the mounting base, and multiple pairs of head gimbal assemblies connected with the drive arms. Each head gimbal assembly includes a thermal assisted magnetic head, the thermal assisted magnetic head has an air bearing surface, a bottom surface opposite to the air bearing surface, and a laser diode module mounted on the bottom surface and adapted to emit a downward laser light to a write element of the thermal assisted magnetic head and an upward laser light, wherein a light shielding structure is provided to prevent the upward laser light emitting to other laser diode modules to generate light coupling, thereby improving thermal stability of the thermal assisted magnetic head.