Abstract: An equation of mechanical sensitivity of pressure-sensitive sensor based on conductive rubber filled by carbon black (CB) was given by general effective media theory. According the equation, mechanical sensitivity was studied by the strain effect, the piezoresistive effect and major parameters of the composite. It concludes that the volume fraction of CB has a great impact on mechanical sensitivity. When the volume fraction of CB is close to the critical volume fraction, the scope of sensitivity is 0.1-11.5 MPa^-1, and the piezoresistive effect is the main sensitive mechanism. When the volume fraction of CB is within the percolation zone, the scope of sensitivity is 0.2-3.6 MPa^-1 , and sensitive mechanism is related to the pressure, i. e. when the pressure is kept at a low value, the piezoresistive effect plays a main role, whereas the pressure is kept at a high value, the strain effect would play a main role. When the volume fraction of CB is within the conductive zone, the scope of sensitivity is 0.3-1.7 MPa^-1, and the strain effect is the main sensitive mechanism.