The monitoring data of a relay protection system in practical application is generally confused, dynamic, incomplete and inaccurate, which belongs to the ‘incomplete information’. This paper researches condition assessment of relay protection system which includes incomplete information. Based on evidence reasoning methods, a comprehensive evaluation for relay protection system without attribute value is provided. By introducing the induced ordered weighted operator, the weight of system status information is determined based on the sequence of each attribute’s performance, ensuring that weight coefficient of the state evaluation model is consistent with system status at any moment. Compared with traditional fuzzy evaluation method by calculation example, Induced Ordered Weighted Evidence Reasoning (IOWER) Method for relay protection systems with incomplete information proves more effective, which could be more specific to reflect system’s degradation. This work is supported by Scientific and Technological Project of China Southern Power Grid (No. GZ2014-2-0049).