In this study, two-year mature satsuma mandarin trees (Citrus unshiu Marc.cv. MiyagaMa Mase) in red soil derived from Quaternary red clay were selected as experimental materials to explore the effects of soil water relative content (SWC) on the growth and polyamines’ content of citrus leaves. SWC was controlled from 30% to 90%. When SWC was 75%，the area, perimeter and width of the leaves all reached the maximal values, which were 12.25 cm2, 13.84 cm and 3.19 cm respectively. And the above 3 indices all showed significant positive correlations with SWC. Putrescine (Put) content was the lowest (228.95 nmol/g, FW) when SWC was 75% while both spermidine (Spd) and spermine (Spm) contents increased by parabolic trends with SWC increase. The maximal contents for Spd and Spm appeared when SWC were 45% and 60% respectively. (Spd＋Spm)/Put ratio showed significant or extremely significant negative correlations with the area, perimeter and length/width ratio of the leaves respectively. (Spd＋Spm)/Put ratio (t) showed a significant positive correlativity with SWC (x) (t＝0.0112x＋0.173, p<0.05 ) when SWC was under 75%. (Spd＋Spm)/Put ratio thus could be selected as a sensitive index for the effect of citrus on red soil water environment.