Based on the surface distributions of the hydrochemical elements(S, O2, PO4 -P, SiO3-Si，NO3 -N, NO2 -N, NH4-N) in the flood and dry seasons in 1959 and 1984. this research on the effects of location changes of the Yellow River estuary in 1964 and 1976 on its hydrochemical environment and biological productivity showed that after the changes, the water tongues of the low salinity and high concentration nutrients moved from their positions near the original Yellow River estuary to the vicinity of the present Yellow River estuary; that the main influential area of the Yellow River brackish water moved to Laizhou Bay; and that the concentrations of all the elements changed. Before the change of river mouth position, NO3-N and NO2-N were exhausted by phytoplankton in many waters, the average of the atomic ratio between total inorganic N and PO4-P was only 4.5, and NO3-N was the main limiting factor for phytoplankton growth in the estuary area. After the change NO3-N concentration increased by 3.7 tinies,the atomic ratio between total inorganic N and PO4-P had reached 36 in the water affected by the Yellow River water. The large increase of inorganic N in the relocated (present) estuary is the main reason for the increase of phytoplankton in that area, Where the Yellow River freshwater and nutrients are now used to full advantage to enhance the biologcal productivity there.