Provides are an apparatus and a method used for detecting space charge in a high-voltage cable joint. The apparatus includes a cable assembly and also an external electrode and a sensor set that are sequentially arranged to be coaxial with the cable assembly. The sensor set is connected with an oscilloscope through a coaxial data wire. The cable assembly is externally connected with a high-voltagepulse generator. According to the technical solution, the sensor set is adopted to detect changes of space charge distribution along with a system conical interface.