The invention discloses a fitting structure for the brush head of a facial brush and a main shaft. The fitting structure comprises an installation part, a large brush head and a small brush head, wherein the large brush head is arranged on the installation part in a sleeving way; a cavity and a No.1 groove which are communicated with each other are formed in the installation part; a connecting piece is connected in the cavity in a sliding way; the connecting piece comprises a fixing rod and two No.1 connecting rods which are arranged at the two ends of the fixing rod; a No.1 through hole is formed in the middle of the fixing rod; a No.2 connecting rod passes through the No.1 through hole; the No.2 connecting rod is provided with a No.2 groove which is connected with the small brush head in a matching manner; separation blades are arranged at the two ends of the No.2 connecting rod; the large brush head is provided with locking grooves which are matched with the No.1 connecting rods; a No.2 through hole into which the small brush head is inserted is formed in the middle of the large brush head. On an occasion where only the large brush head is needed, the vibration of the installation part is only transmitted to the large brush head. On an occasion where only the small brush head is needed, the vibration of the installation part is fully transmitted to the small brush head.