Embodiments of the invention disclose a radioactive detection system and a radioactive detection method, and relate to the technical field of radiation monitoring. By adopting the system and the method, personnel do not need to approach or enter a radiation area or suspected radiation area with an instrument in hand for detection just like that in a traditional measurement method, and the risk is reduced. The system is composed of an unmanned rotor aircraft and a ground control terminal. The unmanned rotor aircraft comprises an unmanned rotor flying platform, and a radiation measuring platform borne on the unmanned rotor flying platform. The radiation measuring platform comprises a storage module used to store all measurement data and detection results, an energy spectrum detection module used to acquire energy spectrum information in a current environment, a multi-channel analysis module used to preliminarily process the energy spectrum information, a data processing module used to integrate and package location information, preliminary processing result data and dose rate monitoring information, and a wireless radio-frequency transmission module used to send a data packet to the ground control terminal. The radioactive detection system and the radioactive detection method of the invention are suitable for remotely detecting the radiation dose rate.