Abstract: There are few methods to identify the type of the nuclear number of medical radioactive source and its activity monitoring at present.An equation （D(E)-C(E)8(E,b)S(S)/4πd² 6^-b） was deduced according Gamma photon attenuation principle.Portable patrol gamma spectrometer was used to monitor the wasted radioactive source to obtain its type and activity.The results showed that its activity was around 4.0×10⁵ Bq.Its type was irregularly stereoscopic V-type radium-226 source.The advantages of the method were fast calculation,which would be useful to calculate the activity of the complex geometric space radiator that is formed by different types of basic element.