By chemical examination in laboratory and test in situ, we found that the CI^- content and SO^2-4 content are higher in Daqing oilfield, and the variation of the soil resistivity is bigger. The soils show strong corrosivity along longitudinal depth to steel equipments. By means of contact test with a reference electrode underground, we measured the distribution of casing protection potential along vertical depth. The results indicate that the casing protection potential curve is smooth, and the protection potential is lower than -850 mV. The casing protection current can polarize up to 10000 cm in depth. The bracelet anode and the casing can installed or repaired simultaneously in the fled with no additional troubles and cost to the conventional field operation, therefore, it is of applicable value.