Long wavelength, weak ionospheric delay and low noise linear combination observational value can realize a quick determination of the integral ambiguity, and all the combined wavelength, the ionospheric delay coefficient and observational noise are determined by the combination coefficients. On the basis of the frequency factor, the ionospheric delay factor and the observational noise factor characterized by the combined wavelength, the ionospheric delay coefficient and the observational noise, the BDS/GPS B1、B2、L1、L2 four-frequency combination observation coefficients suitable for integral ambiguity resolution are obtained. The functional relationships of the combination observation coefficients, the frequency factor and the ionospheric delay factor are obtained under the condition that the observation noise is in the lowest by utilizing the function method. The results show that the combination observational values determined by the three groups, i.e. , and are comparatively long in the combination wavelength, comparatively weak in the ionospheric delay error and comparatively low in the observation noise, which are suitable for integral ambiguity resolution.