Abstract: The online detection system for type identification and activity measurement of radiations in gas or liquid is provided, which can capture the light signals generated by different radiations in real time, and convert the light signals into the electrical signals, so as to realize the online type identification and activity measurement of the radiations based on the waveforms and the time information of the electrical signals of the different radiations. In addition, based on the characteristic that different radiations have different penetration capabilities, the inner-outer two-layer activity measurement structure is designed, which can discriminate the radiations with the same waveform. Therefore, the present disclosure simplifies the radiation activity measurement process, thereby greatly improving the efficiency of the radiation activity measurement.