Abstract: Based on soil and climate of Henan yellow river beach， the paper studied characters of Lucerne (Medicago sativa L.) grasslands Mixed with two species of perennial Grasses[ Smooth Brome(Bromus inermis Leyss) and Sheep Fescue(Festuca ovina L.)] and analysed temporal and spatial dynastics of above-ground biomass and under-ground biomass of mixed grasslands carefully. The results showed that growth dynastics of above-ground biomass and under-ground biomass of mixed grassland appear growth curve with two peaks (ripe period and middle growing period after ripe for above-ground biomass; ripe period and late growing period after ripe for under-ground biomass respectively). Above-ground biomass have maximum increasing periods from heading stage to ripening stage when growing intensities were 11.92gDM/(m2·d) and 14.13gDM/(m2·d) for Lucerne-Smooth Brome mixed grassland and Lucerne-Sheep Fescue mixed grassland respectively;under-ground biomass have maximum increasing periods from tillering stage to elongating stage when growing intensities of roots were 8.53gDM/(m2·d) and 8.94gDM/(m2·d) for two above-mentioned mixed grasslands respectively.