Abstract: According to the characteristics of-50 ℃ ethylene spherical tank made of 07 MnNiMoDR steel, the suitable GER-27 M electrode was successfully developed by selecting slag system reasonably, determining Mn-Ni-Mo alloy system, and applying microalloying technology.A series of technological and mechanical properties tests were carried out on GER-27 M electrode. The results showed that the welding process of this electrode was good at all positions and the diffusive hydrogen content of deposited metal was very low. After a long postweld heat treatment at 40 kJ/cm vertical welding position, the data of-50 ℃ A_KV was still higher than the requirement of technical conditions. The weld metal had low re-heat crack sensitivity, wide heat treatment range and strong brittle fracture resistance.