In this paper, a different valence states(As(Ⅴ) and As(Ⅲ)) and different concentrations (0mg/kg,10mg/kg,20mg/kg,50mg/kg,100mg/kg, 180mg/kg,280mg/kg,450mg/kg and 800mg/kg) of arsenic simulated experiment was set up to study the relationship between characteristics of chemical forms of arsenic and five soil enzyme activities(calatase, polyphenol oxidize, protease, alkaline phosphatase and invertase). Results indicated that AE-As concentration was increased and Ca-As, Fe-As and Al-As concentrations were decreased with the increase of the added amounts of both As(Ⅴ)〖JP〗 and As(Ⅲ). Meanwhile, calcium bound As(Ca-As) occupied the biggest proportion in the total. Soil enzyme activity was characterized by: two valence states of arsenic on the activity of catalase were characterized by inhibition, and inhibition rate was as high as 57.4%. As(Ⅴ) showed the obvious activity of polyphenol oxidase activation, but the As(Ⅲ) had inhibitory effect on polyphenol oxidase. As(Ⅴ) and As(Ⅲ) had effect on the activity of alkaline phosphatase of “low arsenic promotes, high arsenic suppression”. The chemical speciation of arsenic and nonlinear analysis indicated that AE - As had a significant stimulus for sucrase in As(Ⅴ) processing, and its ecological toxicity was the strongest (ED50 was 17.97mg/kg). So for calcareous soil pollution in the north, taking the exchange state As and invertase activity as the main indexes of evaluation was feasible. Through principal component analysis, when the concentration of As(Ⅴ) was up to 50mg/kg, and the concentration of As(Ⅲ) was 10mg/kg, the function of soil microbial structure was changed. The two concentrations can be used as the critical values for affecting soil microbiology properties.