The work aims to analyze influences of depth on hardness and elastic modules by studying loading curve of polystyrene films at different depth, and provide reference for theoretical and application exploration of polymer films confinement effect by studying surface viscoelastic behavior of polystyrene films. Series nanoindentation measurement and analysis were performed to a polystyrene film sample (nearly 500 nm thick) in the method of nanoindentation. The relationship between loading curve and P-h2 varied to different degree at low loading rate. At the loading rate of 0.01 mN/s, 0.02 mN/s, 0.03 mN/s, 0.06 mN/s and 0.1 mN/s, index in P-h2 relationship increased from 1.609 to 1.628 gradually. Relationship between indentation depth and time was obtained, and creep compliance was calculated by holding the maximum load for 60 s. According to Zener model fitting, there were two different viscoelastic structures in the film sample at the indentation depth of 300~400 nm. Moreover, according to unloading curves at different indentation depth, viscoelasticity of sample hardness and reduced elasticity modulus was not uniform in the area with indentation depth of nearly 200~400 nm. There are two different viscoelastic structures at different indentation depth. Widely accepted polymer film model shows that the two structures correspond to free surface layer and bulk layer of polystyrene film sample, respectively.