The invention relates to the field of machine tool reliability testing, and especially relates to a main spindle box fatigue testing machine and a main spindle box reliability testing method performed with the main spindle box fatigue testing machine. The main spindle box fatigue testing machine simulates the cutting force applied to a test piece when a machine tool is actually working by applying the thrust force to the test piece, and the torque applied to the test piece when the machine tool is actually working is simulated by applying the torque to the test piece through the friction force. The test piece is connected to a main spindle box to make the main spindle box drive the test piece to rotate to carry out reliability testing. Accordingly, the load applied to the main spindle box when the machine tool is actually working can be relatively simulated in a real mode; nearly no materials are consumed and no cutter is worn. Reliability test data can be accurately obtained and simultaneously the cost of reliability testing can be reduced. The main spindle box fatigue testing machine and the main spindle box reliability testing method are suitable for popularization and application.