Abstract: Natural capital accounting is one of the key research topics in the field of quantitative sustainability assessment. The ecological footprint, which has reached considerable popularity over the past few years, offers us an opportunity to evaluate the natural capital appropriated by humanity. This paper first introduces the research achievements of the ecological footprint applied to the natural capital measurement. Afterwards a three-dimensional ecological footprint model, the latest development in relevant fields, is introduced in terms of its concept, calculation method and main characteristics. In response to the existing shortcomings and deficiencies we identify, the paper makes a great contribution to the model modification and extension in the following two aspects. One attempt is to modify the calculation methods of three key indicators-regional footprint depth, regional footprint size and regional ecological footprint, so as to avoid underestimating the depletion rate of natural capital stocks, and to avoid the possibility that the ecological deficit and ecological surplus are partly offset by each other because they are in different natures from a perspective of natural capital. The differences exist in results before and after the modification of the three-dimensional ecological footprint model, where a fundamental change is that the classification and measure of the capital stocks and capital flows are extended to the specific land types within a given region. The other attempt is to build three indicators, namely Per Capita Historical Cumulative Footprint Size, Gini Coefficient of Footprint Size, and Theoretical Footprint Size. They are designed for representing the historically cumulative appropriation of natural capital, the inter-regional inequalities in natural capital appropriation, and the impact of decline in natural capital stocks on natural capital flows, respectively. Finally, this paper discusses the limitations of the three emerging indicators, and proposes some priorities for further improvement on measuring the use of natural capital stocks.

Key words: ecological footprint, modification, natural capital, research progress, three-dimensional model