某大型站场阴极保护系统运行一段时间后，阴极保护电位合格率发生大幅度的下降。从现场恒电位仪输出参数、土壤电阻率、预包装高硅铸铁阳极表面形貌和阳极接地电阻等方面对该阴极保护失效的原因进行了分析。结果表明：阳极埋设处土壤较为干燥，土壤电阻率较高，阳极表面的致密氧化物和土壤中的碎石增加了阳极与土壤接触电阻，导致整个系统的回路电阻升高，通过浇水保湿和采用非预包装阳极的方式可以降低阳极的回路电阻。

After the cathodic protection system of a large station had been in orperation for a period of time, the qualified rate of cathodic protection potential decreased greatly. The causes of the failure of the cathodic protection were analyzed from output parameters of potentiostat, soil resistivity, surface morphology of prepackaged high silicon cast iron anode and grounding resistance of anode. The results show that the soil where the anode was buried was relatively dry, so the soil resistivity was high. The dense oxide on the anode surface and the gravels in soil increased the contact resistance between anode and soil. The above-mentioned reasons led to the increase of loop resistance of the whole system. The loop resistance of the anode could be reduced by watering and using non-pre-packaged anodes.