Local viscoelastic properties and a micromechanical structure of polymer hydrogel were studied using transmission acoustic microscopy (AM) with a spatial resolution up to 5 mum. Utilizing various amplitude, phase, and pulse techniques provided by the transmission AM, a velocity and an attenuation of the acoustic wave in the local point of the polymer sample as well as a frequency dependence (dispersion) of these values were evaluated in the frequency range from 30 to 320 MHz. Using these facilities a poly(vinylalcohol) polymer hydrogel for the artificial muscle was studied at the succeeding steps of its manufacturing process of cyclic freezing-thawing. It was found that synchronously, with the increase of the compressional elasticity and acoustic attenuation, a micromechanical nonuniformity of the gel also profoundly enhances it. Fiber-like structures of 10-50 mum width possessing higher elastic modulus appear in the gel which can play a significant role in the macroscopic mechanical properties of the gel.