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 CO

2

/CH

4

and N

2

/CH

4

mixtures were enhanced after synthesis modification. Single-gas permeances of CO

2

N

2

and CH

4

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 CO

2

permeance of 1.16×10

-6

mol·(m

2

·s·Pa)

-1

(equal to 3554 GPU) with an average CO

2

/CH

4

selectivity of 213 in a 50 vol%/50 vol% CO

2

/CH

4

mixture. It suggests that membrane synthesis has a good reproducible. The membrane also displayed a N

2

permeance of 1.07×10

-7

mol·(m

2

·s·Pa)

-1

(equal to 320 GPU) with a N

2

/CH

4

selectivity of 13 for a 50 vol%/50 vol% N

2

/CH

4

mixture. SSZ-1

3 membrane displayed stable and good separation performance in the wet CO

2

/CH

4

mixture for a long test period over 100 h at 348 K. The current SSZ-13 membranes show great potentials for the simultaneous removals of CO

2

and N

2

in natural gas purification as a facile process suitable for industrial application.