  Based on the strong coupling expansion, we reinvestigate two dimensional O(N)
sigma model by the use of Pade-Borel approximants. The conventional strong
coupling expansion of the mass square M in momentum space in beta=1/g^2 is
inverted to give beta expanded in 1/M. Borel transform of beta with respect to
M is carried out and the result is improved as the rational function by Pade
method. We find the behavior of Pade-Borel transformed bare coupling at 18th
order is consistent for N>=3 with that of continuum scaling to the four-loop
perturbation theory. We estimate non-perturbative mass gap at N>=3 and find the
agreement with the exact result by Hasenfratz et.al.
