In this study, the authors used the Brubaker model to investigate the relative contributions of local and remote atmospheric moisture fluxes to the summer precipitation over the Songhua River basin and its interannual variability. Climatologically, due to the prevailing westerly wind in early summer (May–June), remote atmospheric moisture is the dominant contributor to early summer precipitation, accounting for 78.9%. Accordingly, the local evaporation contribution is 21.1%. In late summer (July–August), the East Asian summer monsoon brings more moisture via the southern boundary, so the contribution of remote moisture increases to 86%, and that of local evaporation is reduced to 14%. JRA-55 (Japanese 55-year atmospheric reanalysis) reanalysis data can well capture the interannual variation of summer precipitation over the Songhua River basin, with the correlation coefficients of the observations in early and late summer being 0.73 and 0.83 for the period 1961–2016, respectively. This shows that the moisture flux via the southern boundary caused by the stronger southwest monsoon plays the dominant role in early summer, and the moisture fluxes via the western and northern boundaries are significantly negatively correlated with early summer precipitation. The contribution of local evaporation is not statistically significant. Moisture flux anomalies tend to occur in the early summer with the decay of El Ni?o. In late summer, a significantly positive contribution is made by moisture flux via the southern boundary and a negative contribution by local evaporation. The effect of oceanic forcing on the late-summer precipitation anomaly is not significant, and internal atmospheric variability dominates. The significant negative contribution of local evaporation is due to the significant negative correlation between the surface temperature and precipitation. When precipitation is lower than normal, the surface temperature becomes warmer than normal, so there is more evaporation and a greater contribution from local evaporation to precipitation.