The invention relates to a reliability evaluation method and device based on power transmission and transformation state monitoring devices. The method comprises the steps that according to the effectiveness of various parameter data of a monitoring device, the data effectiveness quantized values of the power transmission and transformation monitoring devices are obtained; according to the uploading conditions of the monitoring device, the communication problem quantized values of the power transmission and transformation monitoring devices are obtained; according to the ratio of the normal running days of the monitoring device, the defect problem quantized values of power transmission and transformation monitoring device bodies are obtained; according to the data effectiveness quantized values, the communication problem quantized values and the defect problem quantized values of the power transmission and transformation monitoring devices, the availability quantized values of the power transmission and transformation monitoring devices are obtained; according to the availability quantized values of the power transmission and transformation monitoring devices of the same type fromthe same manufacturer, the average availability quantized value of the power transmission and transformation monitoring devices of the type from the manufacturer is obtained; according to the availability quantized values of the power transmission and transformation monitoring devices of the same type in the same line, the average availability quantized value of the power transmission and transformation monitoring devices of the type in the line is obtained. Compared with the prior art, the reliability evaluation method has the advantages of being accurate in evaluation and the like.