The RKKY interaction is an indirect interaction between localized spins mediated by conduction electrons of host system. It can realize long-range coupling of localized spins which is very important in the spin-related fields. Therefore, the effective manipulation of RKKY interaction is expected. To this aim, we examine the RKKY interaction in 3-dimensional topological insulator (3DTI) based p-n junction. In this talk, we firstly present a simple introduction of 3DTI. Secondly, it is our model, formulae and method for the calculation of RKKY interaction. Thirdly, we show and discuss our results on this topic. Finally, a brief summary is given.