The flip interconnect process is one of the key technologies for the preparation of infrared focal plane detectors. The Z-direction bias is an important factor affecting the yield of the flip interconnect process. From the point of view of the equipment of flip welding machine, the relationship between the level of flip welding machine and the Z-direction pressure deviation problem is discussed. The measured focal length values of different positions of the calibration block and the collimation cross position of the center point of the calibration block roughly indicate that the upper welding arm is relatively parallel to the lower abasement. In addition, the distances between the two standard blocks and the laser at different positions obtained by the laser beam accurately indicate that the upper welding arm is parallel to the lower abasement, and verify the accuracy of the levelling of the flip welding machine. The method system for studying the levelling problem of flip welding machine is established for the first time, which lays a good foundation for efficiently solving the Z-direction pressure bias problem of flip interconnection process and improving the yield and reliability of infrared focal plane detector.