A comprehensive evaluation of the effectiveness of cathodic protection (CP) of the pipelines at Suligegas-field was conducted by taking the cathodic protection system of a typical block of as an example in terms of the operating status of rectifiers,the insulation performance of joints,the grounding resistance of anode-beds and the lightning protection grounding.Results show that the inefficient isolation for the pipeline protected with the existing grounding system and the bad electrical continuity between the pipelines were the main path responsible for the current-leakage,therby leading to cathodic protection failure.In addition,the seasonal climate change,topographic elevation change,and gas blockage for anode-bedsall contributed to the increase of anode-bed resistance in a periodic manner.After onsite optimization treatment,the CP protection rate of pipeline in that block increased from less than 70% to 100%.The research results can provide guidance for the optimization design and effect evaluation of similar oil-and gas-fields in the future.