  Entanglement entropy in topologically ordered matter phases has been computed
extensively using various methods. In this paper, we study the entanglement
entropy of topological phases in two-spaces from a new perspective---the
perspective of quasiparticle fluctuations. In this picture, the entanglement
spectrum of a topologically ordered system is identified with the spectrum of
quasiparticle fluctuations of the system, and the entanglement entropy measures
the maximal quasiparticle fluctuations on the EB. As a consequence,
entanglement entropy corresponds to the thermal entropy of the quasiparticles
at infinite temperature on the entanglement boundary. We corroborates our
results with explicit computation in the quantum double model with/without
boundaries. We then systematically construct the reduced density matrices of
the quantum double model on generic 2-surfaces with boundaries.
