A mechanical model of a cell was established by using finite element technique to study mechanical behavior of the cell on condition that the plant was water stressed. Based on the biophysical equation, the change of the turgor pressure in cell caused by transpiration was obtained. Then the dynamics equation of turgor pressure was got. The result showed the relation between the turgor pressure and the deformation of the cell. The results also showed that the radius of the cell decreased from 3.55×10-5 m to 2.42×10-5 m nonlinearly when the turgor pressure changed from 200 kPa to 120 kPa linearly; and the deformation was influenced by material mechanical parameter of cell wall. The radius of the cell was 3.58×10-5 m，3.30×10-5 m，3.13×10-5 m respectively as the Mooney-Rivlin constant (C1) was 0.7 MPa， 1.0 MPa，1.5 MPa when the turgor pressure was 200kPa; the radius of the cell was 1.41×10-5 m，1.22×10-5 m，1.10×10-5 m. respectively as the Mooney-Rivlin constant (C2) was 0.10 MPa，0.15 MPa，0.20 MPa when the turgor pressure was 200 kPa. 