Abstract: Microstructure and properties of Zr702 coil MIG welded joints under different welding conditions were studied and analyzed by optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results showed that weld pool and heat affected zone of industrial pure zirconium Zr702 at high temperature in MIG welding process were prone to air pollution, absorbed a large amount of oxygen in the air, oxygen atoms were solubilized in the zirconium matrix in the form of interstitial atoms, which resulted in lattice distortion, greater internal stress and deteriorating performance of welded joints. Rear trailing cover was adopted to effectively protect weld from air pollution and obtain welded joints with good mechanical properties. Welds polluted by air were gray black, while welds with good inert gas protection were silver white. During welding process of industrial pure zirconium Zr702, martensite transformation would occur in heat affected zone. Small arc voltage and fast welding speed could produce lath martensite with finer grain size. When industrial pure zirconium Zr702 was welded with protection of rear trailing cover, and on the basis of ensuring formation of weld, welded joints with good mechanical properties could be obtained by small arc voltage and fast welding speed.