Abstract: Pore size of geotextile was one of the important parameters for application in engineering practices.Two methods were presented for the measurement of geotextile pore size under different pressures: ①Negative pressure method: based on the capillary theory,hydrophilic nature of geotextile,cosθ,was determined by experiment,and then the pore size distribution of geotextile under different pressures could be obtained.②Penetration method: based on the laminar flow theory,the ratio of flow resistance,x,was determined by experiment,and then the characteristic pore sizes of geotextile,O50 and O95,could be obtained under different pressures.The two methods for measurement of pore size are of advantages of convenience,reliability and practicabitity.