Dwarf spheroidal galaxies (dSph) are good targets to search for dark matter annihilation signals through gamma-ray observations. Currently, the most strong constraints on the cross-section at mDM<~100GeV are obtained by observing them with Fermi-LAT. The dark matter distribution in dSphs is difficult to model and the errors in the current constraints are dominated by those in the J-factor. In this talk, I explain the general procedure to determine the DM distribution in dSphs and the variation of the resultant models. I also discuss the effect of the DM spatial distribution on the future gamma-ray search of WIMP annihilation signals using ground-based telescopes.