Objective To evaluate the field application of corrosion downhole tool and explore the prospects for corrosion protection of tube rod. Methods Quality of water produced in oil-well of a block of Yanchang Oil Field was analyzed; and then corrosion rate of oil-well tubes in the water was determined by combining with indoor anticorrosion test. Corrosion protection downhole tool was installed in selected severely corrosive oil-wells. Content of total iron ion in the output liquid and corrosion rate of tubes after the tool was installed were regularly detected. Workover frequency, number of replaced tubes and sucker rods, content of total iron ion and corrosion rate were compared before and after installation so as to evaluate the application effect of corrosion protection downhole tool. Results Before the application, corrosion rate of tubes was 0.199~0.386 mm/a, far higher than the required 0.076 mm/a. After the application, workover frequency decreased from an average of 3.4 times per year to 1.2 times per year, down 64.7%; the average replacement length of tube and sucker rod in each well decreased respectively from 11.6 m/a and 33.6 m/a to 5.7 m/a and 8.0 m/a; total iron ion content decreased by over 42%; Conclusion Corrosive media in the block produced water (oxygen, CO2, H2S, Cl?) are higher and severely corrode oil pipes and tubes. After installation of corrosion protection downhole tool, number of replaced sucker rods, content of total iron ion in output liquid output and corrosion rate all decline significantly. That indicates the tool can effectively slow down the corrosion of downhole string and enjoys application prospect to some extent.