With the reduction of high quality raw materials, white Portland cement (WPC) manufacturers are faced with the problem of lack of resources. In this paper, it is found that adding Na3AlF6 can increase the whiteness of WPC, which is helpful to alleviate the scarcity of resources in WPC manufacture. The effect of Na3AlF6 on the mineral compositions, chroma and hydration of the interstitial phase in clinker was studied by the Rietveld method, scanning electron microscope-energy dispersive spectrometer (SEM-EDS), Raman spectrum, spectrophotometer and calorimeter. The whitening mechanism of Na3AlF6 to WPC was revealed in our work. The results showed adding Na3AlF6 increased the C12A7 content and reduced the C3A content in the interstitial phase. This was beneficial to improve the reflectivity of the sample to visible light, which increased the brightness (L*) of the interstitial phase. Part of Al2O3 of C4AF was captured to form C12A7 in the samples with Na3AlF6, resulting in the decrease of the C4AF content. This weakened the blue light absorption of the samples with Na3AlF6, thereby reducing the yellowness (b*) of the interstitial phase. Therefore, the addition of 1.0 % Na3AlF6 increased the whiteness of WPC clinker. Moreover, adding Na3AlF6 increased the accumulated heat of WPC hydration but prolonged the induction period.