Abstract: The uniformity of the coating covering the electric field detector is a important factor which effects the accuracy of the electric field measuring，it is difficult to satisfy the uniformity requirement by coating manually，and this technology is not stable.In this paper we present a new scheme，in this scheme the ejection gun is driven by a mechanical arm and a damper is inserted between the gun and the spherical sensor，by changing the shape of the split in the damper the paint mass drops to the spherical sensor can be controlled，so the uniformity of the coating can be realized.From the preliminary results，the coating has good uniformity，so this scheme can resolve the coating problem of the EFD spherical sensor at last.