An ICP-AES method for the determination of silicon and phosphorus in ferromanganese was studied. Digesting samples by microwave and all kinds of parameters of the analytical method were optimized, which included selecting the acid and controlling the temperature and pressure of dissolving the sample, confirming analytical spectrum, considering the effect of sample matrix, analytical pH and disturbing elements on the determination results. By optimizing and choosing all kinds of condition parameters, the simultaneous determination of silicon and phosphorus was realized and satisfactory results were obtained. The linear correlation coefficients of Si and P were 0.9998 and 0.9996, respectively. The detection limit for silicon was 0.0060% with recovery of 97.0%-101%. The detection limit for phosphorus was 0.030%. This method is accurate and quick with less reagent dosage and broa linear range. The way of this determination is fit for the determination of silicon and phosphorus with low, middle and high carbon contents.