The present invention discloses an application of high-flavonoid elite germplasm CSR6R6-777 in apple breeding. The present invention seeks to protect use of an apple (Malus domestica) CSR6R6-777 in apple breeding. The deposition number of the apple (Malus domestica) CSR6R6-777 is CGMCC NO.12468. The purpose of the breeding is to obtain an apple germplasm with excellent triats. The apple germplasm with excellent triats is an apple plant that meets the (a) and/or (b) and/or (c) and/or (d): (a) fully red-fleshed; (b) high-flavonoid content in the flesh; (c) high anthocyanin content in the flesh; (d) high antioxidant capacity of the flesh. The present application has great value for functional apple breeding.