Abstract: Forest spatial structure index (FSSI) was defined with commonlyused forest spatial structure parameters (mingling, neighborhood comparison and neighborhood pattern index) as the breakthrough point, referring to the thought of diminishing marginal benefit of CobbDouglas production function in microeconomics and through constructing forest spatial structure production function with mingling, neighborhood comparison and neighborhood pattern index as the “input” and forest spatial structure as the “output”. Meanwhile, forest spatial structure distance (FSSD) was calculated according to the trend of a change from actual forest spatial structure to ideal structure in “threedimensional scatter diagram” of parameters of forest spatial structure. It is verified that FSSI and FSSD can effectively reflect the features of forest spatial structure and the dynamic changes in combination of forest spatial structure parameters, FSSI and the calculation results of FSSD obtained through complete investigation of 75 sample plots with different forest types in 3 different areas in Heilongjiang Province, northeastern China. It can be regarded that FSSI and FSSD perfect and supplement widelyused forest spatial structure parameters. The two can act as overall indicators to describe forest spatial structure states and changes quantificationally.