Abstract: This work proposes the method for preparing 103 Ru, 131 I, 137 Cs, 134 Cs and 40 K mixed radionucllide reference solution by transforming the 103 RuCl 3 existed in general 103 Ru standard solution into Na 2RuNO(NO 2) 4OH, and selecting feasible chemical composition and pH value. The experimental results and radioactivity comparison measurements show that the mixed radionuclide reference solution prepared using the method mentioned ahead is uniform, stable and meets the requirements of the standards radioactivity metrology.