Grassland is the largest distribution area of terrestrial ecosystems on the earth. The plant net primary production (NPP) is an important indicator to reflect the function of the grassland ecosystems. Some research results are reviewed about the effects of plant species diversity, resource availability, grazing, restoration of degraded grassland and climate change on NPP of grassland ecosystems in the paper. These researches show that (1) there are inconsistent conclusions about the relationship between plant diversity and NPP which depends on experimental site, starting status and indicators measured; most of the studies find their "single peak" relationship due to compensation effect of different plant resource utilization niche. However, some studies report that they arepositive and negative relationships when NPP is relatively low and high, respectively. there are many mechanisms to explain their negative correlations including the hypotheses of disturbance, competition and resources availability. (2) Resource availability determines NPP and modifies the relationship between it and plant diversity. Some researches show that there is an interactive effect on NPP between different resources. Improving the level of a limiting resource may reduce its use efficiency, but it may improve the use efficiency of other resources.Nutrient additions improve the productivity of the grassland, while it reduces plant diversity. (3) Grazing affects NPP through changing plant composition and resource availability. Heavy grazing reduces soil nitrogen (N) mineralization rate and NPP, while moderate grazing increases them. In particular, moderate grazing enhances plant diversity due to increase of grassland heterogeneity. (4) Availability of nutrient resources and feedback of plants to it play key roles on NPP in the restoration of degraded grasslands. With the increasing of root biomass, root C/N ratio and the amount of microbial C and soil carbon pool, the net N mineralization rates and N bioavailability rapidly decline during the processes of the restoration. Plant-soil interaction manifestes as negative feedback, which in turn limites the further improvement of plant productivity. NPP may increase with restoration of the degraded grasslands, whereas maximum NPP occurs in the middle or late stages of the restoration. NPP will decline at the late stage of the restoration if there is no disturbance or grazing.(5) Most of experimental warming studies show that there are inconsistent effects of warming on NPP and plant diversity which varies with the different locations and grassland ecosystems due to differences of resource availability and grazing/clipping. In general, the impacts of warming on underground NPP is larger than on aboveground NPP. These results above suggest that they may be easy for the maintenance of the low NPP level through plant diversity conservation and for improving NPP through increasing the availability of nutrient resources, However, how to maintain a high NPP level for long-term without compromising other ecological functions, such as plant diversity loss, is more challenges for us. Compared to international researches in the field, limited data can be available in China now. In particular, there are lacks in the processes and mechanisms of affecting plant primary productivity for grassland ecosystems in China. Therefore, understanding how grazing with future climate change affects plant primary productivity and recovery of degraded grassland ecosystems is a key knowledge to realize the ecological security and sustainable development of economy and society.