This paper defines new atmosphere DOP styles that are TrDOP and IDOP in GNSS relative positioning. From DOP standpoint, it is firstly demonstrated that the efficiency of BDS/GPS fusion precise relative positioning are improved. With the joining of BDS, the values of ADOP, RGDOP and TrDOP decrease efficiently that can be achieved by increasing observing sessions. Moreover, by analyzing TrDOP and IDOP values, it indicates that BDS/GPS fusion is favorable to estimate the tropospheric parameter and has a small impact on estimating ionospheric parameters.