Based on the observed data of strong motion acceleration in California and other states of USA

the attenuation pattern of peak horizontal and vertical acceleration and square root of short time mean squares is studied by regressive analyzing method.795 group（three dimensional） acceleration records are selected to conduct attenuation pattern statistic analysis for PGA and square root of mean short time squares.The attenuation law of the main parameter of PGA in seismic hazard analysis and square root of short time mean squares of acceleration are studied in details in this paper.It is observed that the variance of the square root of short time mean square is less than that of PGA.Thus the square root of short time mean square is suggested to be used for describing the intensity attenuation characteristics in hazard analysis.