Abstract: A system for detecting a core body temperature includes a detection unit, an ECG wave-filter, a body-temperature detection unit, a processing unit, a breath computing and processing unit, a heart-beat computing and processing unit, and a core body temperature computing and processing unit. The detection unit senses the body, and then the ECG wave-filter and body-temperature detection unit measures the electrical cardiac signal and the shell temperature, respectively. The processing unit collects the signals generated by the ECG wave-filter and body-temperature detection unit and transmits the collected signals to the breath computing and processing unit and the heart-beat computing and processing unit, which generate the core body temperature according to the received signals. Accordingly, it is possible to increase the physical parameters for monitoring the vital signs comprehensively. In addition, a method for detecting a core body temperature is also disclosed.