The mechanism of piezoresistive behavior and the improvement of its stabilitv for high—density polyethylene／carbon black(HDPE／CB)composites were studied．The results revealed that the uniaxial piezoresistive behavior resulted from the change in the structure of the percolation network

depending on the filler volume fraction ψand the deformation of the material under pressure．When ψ approached the percolation threshold ψc

with increasing extemal pressure the composites exhibited a positive pressure coefficient(PPC) effect for its resistance．In the ease of ψ far beyond theψc

only a negative pressure oefficient(NPC)effect for its resistance can be obsered．The resistance baseline at zero pressure after unloading shifted upward or downward with the increase of the numbers of compressive cycles

depending on the ψ．The shift of the baseline was related with the residual compressive strain and carl be stabilized by increasing the number of the compressive cycles．Crosslinking of the matrix can restrict the residual compressive strain and stabilize the baseline shift of the resistance-time curve

especially for the composites with a highψ．