SSZ-13 membranes with high separation performances were prepared using ball-milled nanosized seeds by once hydrothermal synthesis. Separation performances of SSZ-13 membranes in CO2/CH4 and N-2/CH4 mixtures were enhanced after synthesis modification. Single-gas permeances of CO2, N-2 and CH4 and ideal selectivities were recorded through SSZ-13 membranes. The effects of temperature, pressure, feed flow rate and humidity on separation performance of the membranes were discussed. Three membranes prepared after synthesis modifications had an average CO2 permeance of 1.16 x 10(-6) mol. (m(2) .s. Pa)(-1) (equal to 3554 GPU) with an average CO2/CH4 selectivity of 213 in a 50 vol%/50 vol%CO2/CH4 mixture. It suggests that membrane synthesis has a good reproducible. The membrane also displayed a N-2 permeance of 1.07 x 10(-7) mol. (m(2). s. Pa)(-1) (equal to 320 GPU) with a N-2/CH4 selectivity of 13 for a 50 vol%/50 vol% N-2/CH4 mixture. SSZ-13 membrane displayed stable and good separation performance in the wet CO2/CH4 mixture for a long test period over 100 hat 348 K. The current SSZ-13 membranes show great potentials for the simultaneous removals of CO2 and N-2 in natural gas purification as a facile process suitable for industrial application. (C) 2020 The Authors. The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.