The present invention discloses a ketone-aldehyde modified resin and the preparation process thereof. The ketone-aldehyde modified resin comprises a ketone-aldehyde modified unsaturated polyester, a ketone-aldehyde modified unsaturated alkyd or the combination thereof, and wherein the said resin has ketone-aldehyde moieties. The process of the said resin comprises the steps of: reacting unsaturated polyester-forming and/or unsaturated alkyd resin-forming monomer components with a ketone-aldehyde resin. The present invention also discloses a coating composition comprising the said resin as well as a coated article. The ketone-aldehyde modified resin and the coating composition achieve significantly improved fast drying effect, while other properties are not observably impaired or even improved.