Objective To analyze the effectiveness and safety of ultrasound-guided small needle-knife in treatment of adult stenosing tenosynovitis of flexor digitorum. Methods 90 adult patients with stenosing tenosynovitis of flexor digitorum in the hospital from November 2017 to November 2018 were prospectively selected. All the cases were divided into T1 group, T2 group and control group by random number table, with 30 cases in each group. All the patients underwent small needle-knife therapy, control group was given traditional blind operation, T1 group was given short-axis ultrasound-guided operation, while T2 group was given long-axis ultrasound-guided operation. During 6 months of follow-up after treatment, the curative effects of three groups were evaluated, and the incidence of complications was recorded; The treatment-related conditions of three groups during treatment were compared, including treatment time, number of treatment, recovery time; The pain degree of diseased finger was evaluated by visual analogue scale (VAS) at each time. Results The cure rate in T1 group and T2 group was higher than that in control group (P<0.05); But there was no statistical difference between T1 group and T2 group (P>0.05); The treatment time, recovery time of capillary filling, sensory recovery time in T1 group and T2 group were shorter than those in control group, the number of treatment in T1 group and T2 group was less than that in control group (P<0.05); There was no statistical difference in the treatment time and the number of treatment between the two groups (P>0.05); The recovery time of capillary filling, sensory recovery time in T2 group were shorter than those in T2 group (P<0.05); At each time after beginning of treatment, the VAS of three groups showed the decreasing trend, the decreasing range of T2 group was the largest, followed by T1 group, and control group was the smallest, the difference among the three groups was statistically significant (P<0.05); There were no complications in the three groups during follow-up. Conclusion Ultrasound-guided small needle-knife in treatment of adult stenosing tenosynovitis of flexor digitorum has high cure rate, short treatment time and less number of treatment. Long-axis ultrasound-guided small needle-knife has better effects, it can relieve pain, recover finger function and have no complications, which is safe and reliable.