Reflectance spectra of eight common scleractinian coral species were chosen to represent the reflectance of corals in the sea area of Luhuitou Sanya Bay in the north-western South China Sea (SCS). Reflectance spectra of these scleractinian corals, ulva and coral rubble were measured using a fiber spectrometer. Then spectral reflectance analysis and derivative spectroscopy were used to study the difference in the reflectance spectrum between reef building scleractinian coral, ulva and coral rubble in this sea area. The results showed that reflectance peak of ulva appeared at 561.4 nm, and its value was as high as 48%; reflectance difference of ulva and scleractinian coral was very significant in 500~700 nm; reflectance of coral rubble was significantly higher than that of coral reflectance spectrum with significant differences. Derivative analysis results showed that the distinguishable bands of scleractinian coral, ulva and coral rubble were as follows: scleractinian coral and ulva, first order derivatives are mainly in 485～487, 505～510, 515～529, 559～578, 587～593, 598～603 and 667～670 nm bands. The second order derivatives are mainly in 494.4～505.7, 524～534.5, 543.6～561.4 and 567.2～579.7 nm bands. The fourth order derivatives are mainly in 515.8～430, 621～627.1, 628.8～635.6, 639.3～645, 661.8～669.8, and 678.4～682.4 nm. First order derivatives of scleractinian coral and coral rubble are mainly in 400～413.7, 414～418, 484.8～486.9, 506～509.6, 514.5～528.9, 576.9～587.6 and 602.7～653.4 nm bands. The second order derivatives are mainly in 451.6～461.6, 564.5～570.7 and 677～685 nm. The fourth order derivatives are mainly in 412.6～425.3, 459.8～467, 467.7～470.6, 535.6～540.8, 583.8～591.4, 654.4～659.8 and 670.8～680 nm bands.