We use the spherical harmonics decomposition of the Fermi gamma-ray maps to search for dark matter annihilation in the Milky Way halo away from the Galactic plane. Small L harmonics are most sensitive for extracting a smooth large scale distribution of gamma-rays, such as the gamma-rays produced in DM annihilation at high latitudes in the main halo of our Galaxy. We perform a template fitting in the $a_{lm}$ space for small L's and find an evidence for a spherically distributed source, additional to typical astrophysical backgrounds. In general, the method of template fitting in spherical harmonics space provides a non-trivial alternative to template fitting in coordinate space and may be especially useful for separating large angular size distributions.