This study was aimed to design a new, accurate and easy-to-use water bath cryo-jaw, and try to solve the problems met in small animals achilles tendon mechanical testing. The muscle-tendon-bony units were fixed in the clamps. SD rats achilles tendon were randomly divided into group A and B. Group A was tested by the newly designed water bath cryo-jaw, while group B was treated by non-water bath cryo-jaw. The mechanical tests revealed that non of the samples of the newly-designed water bath cryo-jaw in group A slipped and fell off, and the achilles tendons were in a physiologically active state, but one of the group B samples slipped and fell off, and the others had the frozen phenomenon obviously. The maximum stress, fracture displacement and Young's modulus of the rats in group A were significantly different compared to those in group B (P<0.05). In conclusion, the new water bath cryo-jaw has more advantages than traditional ones. It exhibits a good simulation in vivo in the environmental conditions for testing the mechanical properties of the achilles tendon.