Adopting a alloy design process of lower C-Mn-Mo-Nb series with right amount of micro-alloy elements such as V, Ti, Ni, Cu and Cr, and using clean steel smelting process and TMCP rolling process, developed successfully X70 thick and high grade pipeline steel heat roll plate. The results of analysis on micro structure and mechanical property showed that its structure was acicular ferrite admixture with ting grain and little inclusion, its band structure was light, and the precipitate was uniform diffusion. The X70 grade pipeline steel has high strength and excellent low temperature toughness.