Using polyvinylidene fluoride (PVDF) as the sensing element of the contact force sensor, the influence of the types and thickness of the upper and lower substrate materials on the sensitivity of the sensor was explored by controlling variables. Through theoretical calculation of piezoelectric equation of piezoelectric material, the relationship between contact force input and voltage output was obtained. The results of finite element analysis show that the thickness and elastic modulus of the upper and lower substrate materials has great influence on the sensitivity of the contact force sensor. When 0.025mm PDMS is used as the upper and lower substrate material, the sensitivity of the contact force sensor can reach 0.527mV/N.