In china, remarkable achievements have already been attained in using radon measurement, especially electrostatic alpha-card method, for groundwater and geothermal prospecting and for engineering geology.weak anomalies of radon usually exist near geological structures containing underground water or geothermal water along fracture zones. The reason is that these structures usually related to some factors affecting the distribution of ra dioactive elements, such as the change of lithologic characters, the rupture of rocks and the high radon content in geothermal water. These structures can therefore be found through detecting the faint radioactive anomalies.The electrostatic alpha-card method invented by the authors is one of the techniques for radon measurement. It has high sensitivity, requires low cost,and is seldom disturbed by topography and other surface features. Hence, it can be used in areas with thick regolith or serious electromagnetic disturbance or noise disturbance, such as cities or town, mountains, factories and mines. The electrostatic alpha-card method serves as an effective and economical method in hy-drogeophysical and engineering geophysical exploration and municipal geophysical exploration.Since 1982, experimental work of electrostatic alpha-card method has been conducted at over 100 places in more than 20 provinces to search for uranium, gold, oil and gas, to detect the leakages of reservoirs, to investigate vein rocks, to delineate boundaries of different rock bodies, and to seek for groundwater and geothermal water. Facts show that this radon-measuring technique yields good geological results snd economic benefits.