Abstract: Through comparing the measurement methods of humidity for each component of plastic mixtures， a humidity testing scheme of plastic mixtures was designed based on a drying weighing method combined with the test method of GB/T 19277.1—2011. This method does not destroy plastic mixtures to obtain relatively accurate measurement results. The results indicated that the difference between the measured mass humidity of the plastic mixture obtained from the conventional drying weighing method was 3 %~5 %. It is difficult to make rapid changes in the mass humidity when the difference reached around 9 %. There is a three-stage humidity change process for plastic mixtures as follows： constant rate， deceleration rate， and residue. The Boltzmann function could fit the trend of constant rate and deceleration rate better in the humidity change stage of plastic mixtures. The on-demand water replenishment is more advantageous to the aerobic biodegradation activity， which is in better agreement with the requirements of the national standard for the aerobic biodegradation test of plastics. According to the change curves of moisture mass dissipation of plastic mixtures at three gas-flow rates， the calculation method of the change curves of moisture mass dissipation at arbitrary gas flow rates was obtained.

Key words: plastics, weighing method, biodegradation, industrial composting, organic soi, data fitting, moisture content