The basic pyrolysis behaviour of ethylene vinyl acetate(EVA) copolymer, which is often used as a lamination agent in solar modules, was investigated in thermogravimetry, differential thermal analysis(DTA) and thermovolumetry. The TG analysis showed that the EVA pyrolysis can be accelerated under the partial oxidizing atmosphere but the end pyrolysis temperature must be higher than in nitrogen, to eliminate the coke formed. Meanwhile, a strong exothermal peak occurs at about 450℃ under the air condition and gets weaker obviously at the oxygen content lower than 10 vol.%. The mass balance of EVA pyrolysis was given through thermovolumetry with the output of 10 wt.% permanent gas, 89.9 wt.% condensate and 0.1% residual coke. Besides, the composition of the permanent gas and condensate at different pyrolysis stages were analysed and interpreted on the known pyrolysis mechanism.