The invention provides a test object connection device of a mechanical fatigue testing machine. The device comprises a rotating mechanism, a pushing rod and a sensor, wherein the rotating mechanism isarranged between the pushing rod and the sensor, and the rotating mechanism is used for driving the sensor to rotate up and down around the pushing rod. Compared with the prior art, a sensor supportand a connecting rod are hinged through a hinge pin; and when the fatigue testing machine is used to perform a fatigue performance test on a test object, a pushing head is perpendicular to the test object all the time due to hinged connection, the force measured by the sensor is force actually acting on the test object, therefore, a measurement error is avoided, and the accuracy of test data is greatly improved.