Nitrogen-doped porous carbons with BET surface area of 1068.2-3314.5 m2/g and nitrogen contents of 3.2–6.5% were prepared from solid waste grape-seed via NaNH2 as activator and nitrogen source at lower activation temperature. The activation mechanism of NaNH2 on hydrothermal carbon precursors was first explored by thermodynamic analysis and TG-IR, which provided theoretical support for pore-forming of carbon materials. Maximum CO2 and CH4 adsorption capacity at 273 K and pressure of 101 KPa was 5.42 and 1.76 mmol/g respectively, which is higher than that of majority of solid waste derived carbons reported in literature. IAST selectivities of GS-3-450 with the largest BET surface area for CO2/CH4 (40v/60v), CO2/N2 (15v/85v), CH4/N2 (50v/50v) were found to be 20.3, 71.4, 6.0 under 101 kPa and 298K respectively. The competitive adsorption of GS-3-450 for CO2/CH4 (40v/60v), CO2/N2 (15v/85v), CH4/N2 (50v/50v) gases mixture were examined through breakthrough experiments, and the results showed the CO2 breakthrough time was longer than that of CH4 and N2, which was beneficial to the separation of CO2 from gases mixture. CH4 adsorption-desorption studies for 8 cycles revealed that the material exhibited excellent recycling stability. The lower temperature preparation method, excellent BET surface area and total pore volume and excellent CO2 and CH4 adsorption ability make it having a very good potential for the capture of CO2 and CH4.