The carrier injection process of polymer light-emitting diodes (PLEDs) with MEH-PPV(poly［2-methoxy，5-(2-ethylhexoxy)-1，4-phenylene vinylene］) as the light-emitting layer, was investigated using impedance spectroscopy, capacitance-voltage (C-V) and capacitance-frequency (C-F) techniques. The diodes have the configuration of ITO/PEDOT/MEH-PPV/Ba/Al. The experiments showed that there is an ohmic contact between electrodes and MEH-PPV, and holes and electrons injected from the cathodes are unbalanced. Charged traps in the MEH-PPV result in space-charge under positive bias, and the trap concentration was estimated at about 3.75×1016cm-3.