The invention provides a force measurement sensor and a method used for measuring the pressure which a prestressed cable and a bridge bearing are loaded. The force measurement sensor comprises a compound elastomer consisting of a rigid liquid storage and pressure body having a cavity and the inert liquid in the cavity of the rigid liquid storage and pressure body. A nozzle tip seat is fixed on the rigid liquid storage and pressure body. An open hole on one end is communicated with the inert liquid. The other end of the nozzle tip seat is directly or indirectly provided with a measuring sensor. The measuring sensor is communicated with a measuring circuit connected outside. The force measuring method is that one part of the external force is received by the rigid liquid storage and pressure body inside the compound elastomer; the other part of the external force is received by the inert liquid inside the compound elastomer; the measuring circuit measures the change of the pressure of the inert liquid according to the electrical signal sent out by the measuring sensor. The equation of Y=AX<2>+BX-C is used to calculate out the force received by the sensor, or the force received by the sensor is got by checking the figures. The height of the force cell is small, and the outside diameter of the force cell is small. The force measurement sensor is compact and stable permanently, and can resist the environmental impact. The force measuring method is simple and reliable.