In terms of the reliability analysis of ultimate longitudinal strength of naval ships in-service based on the data of pitting corrosion recorded, the non-probabilistic reliability analysis theory was introduced. A new method to analyze the ultimate longitudinal strength reliability under the present condition was put forward for hull structures，the non-probabilistic reliability analysis model was established, and the application of non-probability reliability method on condition assessment of hull structure was analyzed. Results show that the proposed theory overcomes the defects that relied too much on the corrosion sample library， the consequence tends to be more realistic than the deterministic method, and the non-probabilistic reliability analysis theory has a good application prospect for condition assessment of naval ships.