The Yanchang oilfield is famous for its ultra-low permeability which is the main factor leading to low productivity, water cut rising fast, high capacity diminishing and low recovery. In order to solve these problems, a new agent has been selected through 22 kinds of agent by static de-oiling experiments, and agent interfacial tension experiments, and the salt experiments and core flow experiments, and its affects has been proved in a water injection zone of Wang214 field in Xingzichuan oilfield. The effects is obvious, for the crude oil production has been improved by 40%, and the oil recovery factor has been enhanced by 6.08%, the cumulative oil is 13 555 tons, and the input-output ratio is 1∶5.06. This displacing agent has a broad prospects in ultra-low permeability reservoirs for the features of high removal efficiency of oil, low interfacial tension, calcium salt tolerance performance, good solubility, high oil displacement efficiency and low cost, which can change the reservoir rock wettability, reduce the injecting pressure, enhance oil recovery, improve the production effects, and have a high percentage of input and output.