Objective To study the effects of cement base with different thickness on the stress distributions of restored tooth by finite element method. Method A threedimensional finite element model of a restored first mandibular molar with class 1 cavity was developed based on Micro CT. The thicknesses of cement base with lightcured glass ionomer (Vitrebond) and selfcured calcium hydroxide (Dycal) were chosen as 0.5 mm, 1.0 mm, 1.5 mm and 2.0 mm, respectively. Occlusal load of 250N was applied to compare the peak maximum and minimum principal stresses of the tooth, restoration and cement base in each model. Results With Dycal of 2mm, the peak maximum principal stress of the tooth was higher than its tensile strengths, and the peak maximum/minimum principal stress of the cement base was both higher than its tensile and compressive strength. Moreover, the peak maximum principal stress of the restoration was about 90% closer to its tensile strength with Dycal of 1.5 mm and 2 mm. With Vitrebond, it also showed that the peak maximum principal stress of the tooth, restoration and cement base appeared in the models with cement base of 1.5 mm and 2.0 mm. Conclusions To prevent the failure in restored tooth, it is advised to use thinner cement base, and the thickness of cement base should be considered from 0.5 mm to 1.0 mm in clinic.