The invention provides a power transformer-used silicon steel sheet iron core magnetic performance detection system and a detection method. The system comprises a to-be-detected excitation iron core, a compressive stress loading and measuring module arranged on the to-be-detected excitation iron core, a variable-frequency excitation power unit, an iron core magnetic performance measurement unit and a DC bias unit. The method comprises steps: the magnetic performance detection type of the to-be-detected excitation iron core is judged; the relationship between each item of magnetic performance and other detection items of the to-be-detected excitation iron core in different conditions is detected; and a detection report is issued. The system and the method provided by the invention is low in cost, flexible in arrangement and simple in structure and realization process; simulation on harmonic excitation conditions of the engineering-used large power transformer iron core, DC magnetic bias operation conditions and iron core compressive stress conditions is effectively and accurately realized; and a reliable and accurate basis is provided for evaluating the no-load excitation performance of the engineering-used large power transformer in different operation working conditions.