Abstract: The large thickness plate DILLIMAX690E was welded with domestic welding wire by using the automatic ultranarrow-gap GMAW technology in this research.And based on the relevant national standards,microstructure,micro-hardness and macro-visage of 690 steel welded joints were analyzed by the tensile tests,bending and impact tests.The results showed that the large thickness plate DILLIMAX690E which belonged to the classification which is known as high-strength low-alloy quenched and tempered steel had been welded successfully by the automatic ultra-narrow gap GMAW technology with low welding hea tin-put.Comprehensive mechanical properties of welded joints were ensured with good fusion and forming.Meanwhile,the high efficiency welding was achieved.