The invention proposes a magnetic domain in-situ observation system in a reciprocating-type friction process, and the system comprises a pin-block reciprocating friction test bench which comprises a test bench pedestal comprising a longitudinal base and a lateral cubic base locate at a front side of one end of the longitudinal base; a lifting mechanism which is installed on the longitudinal base in a manner of moving up and down; a reciprocating friction mechanism which comprises a longitudinal moving part, a lateral moving part and a reciprocating sliding block, wherein the longitudinal moving part is fixed on the lifting platform, the lateral moving part is installed on the longitudinal moving part through a longitudinal sliding block pedestal, and the reciprocating sliding block is disposed on the lateral moving part; a loading mechanism which comprises a weight pin, a rolling wheel, a rope and a weight pallet, wherein the weight pin is fixed at the rear end of the reciprocating sliding block, and the rope is wound around the rolling wheel; a displacement measurement mechanism which comprises a displacement sensor, wherein the displacement sensor is installed on the lifting platform through a support; a sample clamping mechanism which is provided with a lateral sample clamp; and a microscopic observation system which comprises a microscope, a CCD image sensor, and a computer.