The switching field of a polymer dispersed liquid crystal (PDLC) film depends on a number of factors. In this paper, the switching mechanisms of a polymer dispersed liquid crystal film are studied both theoretically and experimentally. The theoretical model is based upon the balance of elastic and field torques in ellipsoidal droplets. It is used to describe how switching field depends on droplet size and shape, and to calculate the switching field analytically. In experiment, the switching field is determined from optical transmittance measurements. The possible switching mechanisms are discussed from the comparison between experimental and theoretical results on the switching field as a function of temperature.