This research examines the growth of Chlorella sp. microalgae under nutrient limitation (10–200 mg NaNO3 L−1 and 10–70 mg K2HPO4 L−1) and different light intensities (60–450 μmol photons m−2 s−1) for achieving maximum carbohydrate content and biomass productivity using Response Surface Methodology (RSM) technique. According to the results, nutrition limitation had considerable effect on carbohydrate accumulation especially phosphorus concentrations; as in constant light intensities, maximum carbohydrate content was obtained in minimum concentration of K2HPO4. Under favorable circumstances; i.e. K2HPO4 = 10 mg L−1, NaNO3 = 105 mg L−1, and light intensity = 255 μmol photons m−2 s−1 the highest carbohydrate content by 60.9% was achieved. Moreover, Supercritical Water Gasification (SCWG) of carbohydrate enriched microalgal biomass is able to produce much more hydrogen gas in comparison to the basic microalgal biomass. In addition, a 1.85 times increase in amount of produced gas is appeared as a result of a change in biochemical composition of the microalgal biomass. •Nutrient limitation is an effective strategy for increasing carbohydrate accumulation.•Higher light intensity and nutrient concentrations leads to higher biomass productivity.•Under optimized condition, the maximum carbohydrate productivity of 128 mg L−1d−1 was achieved.•Application of enriched carbohydrate microalgal biomass in SCWG caused up to 4.63 times increase in amount of hydrogen production.