An electrochemical air dehumidification system with polymer electrolyte membrane (PEM) was developed. The system performance under various operating conditions was investigated experimentally. A semi-empirical prediction model was also developed with multi-parameter linear regressions. Results showed that the novel system could dehumidify the air flow, with a humidity decrease from 90% (inlet) to less than 30% RH (outlet) under a 3 V electric field, which is promising as it can achieve an independent, portable and energy-efficient moisture removal. The steady-state dehumidification performance derived was 80 kg/(kW h.m(2)), or 54 kg/ (h.V.m(2)), which were advantageous to current electrochemical dehumidifiers. Specially, this simple element has a volume of only 0.001-0.01 parts per thousand of traditional ones, which is also suitable for cascading or multilevel assembly to satisfy various requirements for commercial and industrial applications. The moisture transfer, mainly caused by the electrolysis (+), electro-osmosis (+) and back diffusion (-), increased significantly with the increases in anode-side air humidity and flow rates. When the inlet air humidity increased from 70 to 90%, the dehumidification rate increased about 1.5-2 times. However, only 30% of total power input was effectively used in current element, and the rests were lost, leading to a relatively low system COP (approximate to 0.33). The main reason was that the back-diffusion mass transfer was found to be up to 2.3 times larger than expected, causing by the high moisture content in cathode-side layers (mainly the diffusion layer), which seriously deteriorated the system performance. Therefore, enhancing the diffusion layer performance may help to optimize the dehumidification efficiency effectively. The suggested measures include improving the structure, changing the internal surface parameters or adding microporous layers, etc.