In order to evaluate the risk probability of brucellosis carried by adult sheep introduced by purified farms within local province，a“scenario tree”was drawn to establish a risk assessment model for introduced animals without laboratory test or with one or two laboratory tests，the distribution values of relevant parameters of the model were obtained by simulation calculation with @Risk software. It was found that the probability of introducing brucellosis via an adult sheep was 0.048%（95%Cl：0.024%-0.083%）、0.306%（95%Cl：0.196%-0.447%）and 1.975%（95%Cl：1.454%-2.587%），respectively through the scenario models including“double detection”，“single detection”and“no detection”. As it was compared that the average risk of introducing adult sheep under“no detection”model was 6.5 times larger than that under“single detection”and 41.1 times than that of“double detection”. It was found that，through sensitivity analysis，the main protective factor included the sensitivity of diagnostic test，with correlation coefficient of -0.89；and main risk factor included the group and individual prevalence，with the correlation coefficients of 0.40 and 0.17 respectively. In conclusion，the entry risk of brucellosis could be effectively reduced through reducing the group and individual prevalence and advocating detection before entering into population.