Atmospheric nitrogen (N) deposition has profound effects on the biogeochemical cycling of carbon (C) and N. The interactions between C and N can affect biogeochemical cycling by modifying soil enzyme activities; however, these interactions still need to be explored. Using a factorial glucose and ammonium nitrate addition experiment, we investigated how C, N, and their interactions affect soil enzyme activities and enzymatic stoichiometry in an arid, hot valley. The enzymes in this survey were involved in the acquisition of C (β-1,4-glucosidase), N (leucine aminopeptidase and chitinase), and phosphorus (P) (acid phosphatase). C:N:P enzymatic stoichiometry was calculated as ln(β-1,4-glucosidase):ln(leucine aminopeptidase+chitinase):ln(acid phosphatase). The results showed that interactions between C and N significantly affected activities of β-1,4-glucosidase, acid phosphatase, and leucine aminopeptidase. C addition decreased β-1,4-glucosidase activities by 31.4% in soils collected from control plots, but increased β-1,4-glucosidase activities by 54.4% in soils collected from N addition plots. The effects of C addition on activities of acid phosphatase and leucine aminopeptidase in soils collected from control plots were relatively small (increased by 102.4% and 28.8% respectively). In comparison, C addition increased acid phosphatase and leucine aminopeptidase activities by 302.2% and 68.8%, respectively, in soils collected from N addition plots. The promoting effects of C addition on β-1,4-glucosidase and acid phosphatase activities were positively correlated with soil initial N availabilities. Chitinase activities increased by 53.7% under C addition, but did not respond to N addition. C and N also interacted, affecting the stoichiometry of C:N and C:P acquisition activities. C addition decreased C:N acquisition activities by 16.9% and C:P acquisition activities by 19.9% in soils collected from control plots. However, the effects of C addition were small in soils collected from N addition plots with decreases of C:N acquisition activities by 1.9% and C:P acquisition activities by 5.8%. The results revealed that interactions between C and N play a critical role in regulating soil enzyme activities in this arid, hot land and may be a key factor determining soil ecosystem functioning.