Polymer light emitting diode (PLED) with an ITO/MEH-PPV/Al structure were prepared by spin coating method on the ITO (indium tin oxide)/glass substrates, using poly(2-methoxy-5-(2-ethylhexoxy)-1,4-phenylenevinylene (MEH-PPV) as the light emitting material. The dependence of heat treatment on the electrical and optical properties for the prepared PLED samples were investigated. The luminance decreased greatly from 630 cd/$m^2$ to 280 cd/$m^2$ at 10V input voltage as the heating temperature increased from $65^{circ}C$ to $170^{circ}C$. In addition, the luminance efficiency was found to be about 2 lm/W for the sample heat treated at $65^{circ}C$. These results may be related to the interface roughness and/or the formation of an insulation layer, which is caused by the reaction between electrode and MEH-PPV organic luminescent film layer.