Litter and understory vegetation play important roles in soil carbon and nitrogen cycles in forest ecosystems. However, the mechanism of the effects of litter and understory vegetation on soil carbon and nitrogen hydrolase activities remains unclear in subtropical Chinese fir forests. In this study, four different litter and understory treatments (litter and understory vegetation removal (LR+UR), litter removed but understory vegetation intact (LR+U), litter doubled and understory vegetation intact (LD+U), litter doubled and understory vegetation clipped but left in situ (LD+UC)) were established in subtropical Chinese fir plantations. We studied the effects of litter and understory vegetation on soil environmental factors (soil temperature (ST), soil moisture (SWC), soil acidity (pH), soil nitrate nitrogen (NO₃^--N), ammonia nitrogen (NH₄⁺-N), and dissolved organic carbon (DOC)) and soil carbon and nitrogen hydrolases (β-1, 4-glucosidase (βG) and β-1, 4-N-acetyl-glucosaminidase (NAG)) activities in order to reveal the mechanism of the effects of litter and understory vegetation on soil carbon and nitrogen hydrolase activities. The results showed that: (1) litter addition increased soil pH, NH₄⁺-N content, and hydrolase activities compared to the LR+U and LD+U treatments, although the effects were not significant (P > 0.05). (2) A comparison of the LR+UR and LR+U treatments showed that understory clipping significantly decreased the DOC content and βG activity (P < 0.05) and tended to reduce SWC, pH, NH₄⁺-N, and NAG activity. (3) Litter addition with intact understory significantly increased SWC, pH, DOC, and NH₄⁺-N content, and enhanced βG and NAG activities (P < 0.05). The understory clipping in situ treatment was even more effective at increasing βG activity, NAG activity, SWC, and DOC than the understory unclipped treatment. However, neither LD+U nor LD+UC treatment had a significant influence on ST and NO₃^--N content compared to the LR+UR treatment. (4) Soil βG and NAG activities had significant positive correlations with SWC and DOC contents (P < 0.01). In conclusion, litter and understory vegetation affected βG and NAG activities by regulating SWC and increasing DOC content. The enhancement of βG and NAG activities may in turn increase DOC content by stimulating decomposition of soil organic matter.