The evaluation of the product quality level is the premise of quality improvement. When the quality characteristics are not related with the quality cost, or the relationship between them is not obvious, the evaluation results obtained from different evaluation methods of product quality level have not significant difference. But in the practice, the evaluation results are largely different when adopting different evaluation methods of product quality level. In this article, various evaluation methods are comparatively studied through examples, and the result shows that under some particular situations, the evaluation method of quality loss function is better than other methods.