With four-year-old outer petals of Yulania×soulangeana on different flowering stages as materials,floral color index,anthocyanin,flavonoid,soluble sugar content,pH index and relative enzymes were studied to explain the chromogenic mechanism of floral color in Yulania×soulangeana.The results showed that:(1)As the flowering stage progresses,PAL and CHI activity become lower,pH index of petals are higher,and the contents of soluble sugar,anthocyanin and flavonoid become lower.The light of the petal strengthened,the red chroma,multi-colored chroma decreased.And every parameter in different flowering stages had significant difference.(2)With correlation analysis the variation of soluble sugar content,PAL and CHI activity and anthocyanin and flavonoid contents showed significantly positive correlation.The variation of pH index,the lightness L^*-value and anthocyanin and flavonoid contents showed significantly negative correlation.The chromatic component a^*-value and anthocyanin contents showed significantly positive correlation.In conclusion,the contents of anthocyanin and flavonoid can affect the floral color of Magnolia×soulangeana.The petals of different color need soluble sugar content,PAL and CHI,pH index to complete normally physiological metabolism that regulate anthocyanin forming,and change petal color of Yulania×soulangeana.