Based on the working principle of Si piezoresistive force sensor

and mini-changes of length of solid and liquid thermal expansion are measured by using force sensor

then the thermal expansion coefficients are measured

it is less than 2 % that the experimental results compared with recognized value.This method realizes electronic measurement of the mini-change of length

makes the measurement more simple

and improves the traditional measuring method

and extents the application of sensor in the physics experiments.