The objective of this study is to investigate the influence of various tissue loads on the working characteristic of the ultrasonic scalpel, including working frequency, input admittance and reflection factor. Ex vivo animal experiments are carried out and relevant discussions of experimental results are provided. Admittance measurement results show that different tissue loads have different effects on a scalpel's working ability. Soft tissue makes the working frequency decrease and bone tissue makes it increase. Radius of admittance circles and reflection factor are also different. Equivalent circuit model is found and with a least-square parameter identification method, input admittance of ultrasonic scalpel with different tissue loads is solved. Results show that admittance circle radius is determined by the value of R1. Changes in L1 and C1 contribute to the shift of working frequency. This study will help decrease the sensitivity of ultrasonic scalpel to loads and greatly increase surgery efficiency.