Abstract: We studied the changes of the morphology, chlorophyll contents and spectral reflectance of a Pinus densiflora forest that was damaged by Dendrolimus spectabilis in the spring in Zhaoyuan County, Shadong province. The results showed that the pine caterpillar-grazed red pine trees had bad growth, and their needles faded or even turned dead. We divided the damaged trees into five levels based upon the density of pine caterpillars, defoliating degree, growth status and needle colors. The chlorophyll contents decreased gradually as the damage level increased. The inflexion point of the red band shifted toward the short-wavelength end of the spectrum, a phenomenon called"Blue Shift", in the red pine forest damaged by pine caterpillars. This"blue shift" can be quantified by the values of Rs,Ro, λp,λpr,λo and R550-680.