Abstract: According to the research and practice on nutrient cycle of black locust forest stands in the area of gulled loess plateau,some key problems in the research of nutrient biogeochemical cycle have been discussed.It is pointed out that in the processing of nutrient circulation flux measurement there exist some errors and problems,such as in the measurement of annual standing stock,nutrient returning amount with litter,nutrient returning amount with atmosphere input and rainfall eluviation action in the whole growth process.During the presupposition of model establishment,the influence of tree ages should be considered in the calculation of nutrient absorption amount.In the processing of nutrient efficiency using measurement,the higher estimation errors of tree nutrient utilization efficiency could be overcome with the revised Chapin index,which could really reflect the nutrient using condition in each growing stage of trees from the point of nutrient circulation utilization.