Abstract: The "critical divergence", "critical opalescence", intensive oxidation, alterable dielectric constant, extraordinary solvating power and structure character of supercritical fluids are reviewed,and geological applications of supercritical fluids are discussed. The macrocosmic properties of supercritical fluids are tightly concerned with microscopic structure. Supercritical fluids are an important factor in many geological processes. Supercritical fluids play an important role in the processes of fluid-rock reaction and tectonics evolution,participate reaction and provide energy foritin the formation of oil and gas,are profit to migration and enrichment of elements in hydrot hermal formation of ore deposits,and greatly affecton generations of seismand magma.Supercritical techniques(supercritical extraction and super critical water oxidation)can improve recovery ratio of ore and dispose efficiently different kinds of wastes.It was proposed that further work would be done in the fields of supercritical reaction,investigation of deep-earth processes and development of supercritical techniques in environment algeology.