Induced radionuclides generated from the probe which is bombarded by proton beam will turn the detector into a typical external irradiation radiation source. Thus, it is beneficial for developing radiation protection to calculate the types and the activities of radionuclides. Here we applied both a theoretical analysis and a Monte-Carlo method to compute the induced radioactivity in a copper probe irradiated by proton beam. Various kinds of radionuclides saturation activity obtained by these two different methods were compared. The comparisons of the results cast by the two methods show the similar saturation activities for 63 Zn and 65 Zn. However, the Monte-Carlo method conducted by the software FLUKA is able to provide a more complete consideration on nuclear reaction, and to calculate both the direct and indirect radioactivity under different irradiation time. Furthermore, by employing the FLUKA Monte-Carlo program, the induced radioactivity of three types of probe materials (Cu, Ta and W) under low-energy (below 20 MeV) proton beam irradiated were also separately simulated and tantalum is considered as the best material for low-energy proton interceptive diagnostics probe due to the higher energy threshold of nuclear reaction and the lower radioactivity.