Formation of melt ponds is pervasive on sea ice and ice shelves prior to their disintegration. Such process should be critical for the deglaciation of a snowball Earth but has never been considered in previous studies. Here we develop a module to explicitly track the initiation, growth and refreezing of melt ponds on ice. Incorporation of the module into a climate model indicates that it provides a strong positive feedback to the climate, and previous studies seriously overestimated the threshold CO2 at which a snowball Earth deglaciates. At CO2 level of 0.1 bar and without the melt pond effect, the annual mean equatorial surface temperature is only -7.7 °C, far from deglaciating. However, this temperature increases to 6.1 °C in a few tens of years once melt pond effect is turned on. The results also demonstrate unambiguously that the deglaciation of snowball Earth should start from the equator, although seasonal melt ponds may appear first in the subtropical regions.