The PEEK/PEI/PES plastic alloys were processed by twin-screw extruder at 370°C separately with five mass ratios of 70/30, 70/25/5, 65/30/5, 60/30/10. The flame retardant of plastic alloys were investigated by experiments, their results showed that, the oxygen index declines when PES was added, the oxygen index of plastic alloy with mass ratios of 70/30 is higher than that of pure PEEK or PES, lower than that of pure PEI, which the oxygen index is 37.1%. The volume resistivity plastic alloy with mass ratios of 60/30/10 is 3.72×1017Ω·cm, which is higher than that of pure PEEK and PES for two orders of magnitude, and the insulation performance of PEEK is improved significantly by alloying.