Singularity problems in a tripiezoelectric body composed of three dissimilar materials bonded along two parallel interface are analyzed in the framework of linear piezoelectricity.Each layer of the trimaterial is assumed to possess the symmetry of a hexagonal crystal in the 6mm class and subject to electromechanical loadings which produce in-plane electric fields and out-of-plane displacement. Based on the complex variable theory and the method of alternating technique, the solution of electric field and displacement field is expressed in terms of explicit series form. Some piezoelectric constant combinations to make the composite perform the largest response of electric field have been found, and can be used to build a relatively effective sensor in a piezoelectric composite material system.