A kind of rotary fiber Bragg grating（ FBG） viscometer is designed for liquid viscosity measuring. The finite element analysis on the main structure of FBG rotary viscometer show that the maximum strain of sensing element is 2. 578 × 10- 6

3. 868 × 10- 6

7. 502 × 10- 6and the torsion angle is 1. 32°

2. 04°

3. 83°

when at the same rotation speed with 44 r / min and different viscosity with 0. 5

0. 75

1. 5Pa·s. Results show that the change of the liquid viscosity values can affect the torsional deformation of torsion sensor

and this is a certain linear relationship. The finite element analysis provides the basis for researching the working principle and improving the structural properties of sensor.