According to the problem of complex structure and verbose operation of SCD file in smart substation, C# model for smart substation secondary system is designed. The model consists of SCDDocument class, IED class and SubNetwork class, namely responsible for SCD file operation, IED data extraction and subnetwork data acquisition. Attribution and functions in each class are designed. The feasibility is verified by SCD file in real smart substation and C# verification programming. It is convenient to read data from SCD file and to manage data in SCD file in object-oriented way by means of model construction. Besides, it is also a solution for SCD file operation design in software development.