This paper describes a method of calibrating the absolute spectral sensitivity of silicon photovoltaic cell. The cell was used for measuring minute radiant power, irradiance and radiant intensity of radiations, ranging from 0.4 μm to 1.1 μm. It was also used for measuring the external quantum efficiency of electroluminescent devices. The sensitivity of the system is higher than that of the conventional thermopile by three orders of magnitude. By incorporating with an integral sphere, it is very convenient to measure the radiant power, ranging from 6.3 nW to 310 mW, of any uniformly or non-uniformly distributed source.The maximum spectral efficiency Km was determined by using this system, and the accuracy of radiometrie system and photometric system was discussed. Finally, the measured optical parameters of some light-emitting diodes were examined.