The invention provides an anti-expansion method of a copper foil in the plasma treatment process of a rigid-flex board. The method includes an adhesive tape bonding step, a lamination step, a copper foil etching step, a plasma treatment step and a polyimide adhesive tape removing step. The adhesive tape bonding step is used for bonding a polyimide adhesive tape on a flex board area before lamination. The lamination step is used for adopting a foil covering method to conduct lamination to cover the copper foil on the rigid-flex board, the copper foil is covered on the flex board area, and the copper foil is directly contacted with a covering film of the flex board area. The copper foil etching step is used for removing the copper foil on the flex board area in etching mode through the image etching mode after lamination. The plasma treatment step is used for executing the plasma treatment to achieve dirt removing. The polyimide adhesive tape removing step is used for removing the polyimide adhesive tape. By means of the method, copper foil expansion cannot happen in the plasma treatment process and the covering film cannot be damaged due to the fact that the high temperature resistant polyimide adhesive tape is bonded to the flex board area to protect the soft board area before lamination, and the copper foil on the flex board area is removed in etching mode after lamination.