Break of highly filled composites based on high-density polyethylene and rubber particles was studied by acoustic emission method. Found that the destruction of the composites can occur when a single unsafe defect is appear, provided that the value of the critical crack opening of the matrix polymer is less than 520 microns. If this value is more than 520 microns, composites deform plastic after the appearance of unsafe defect. The destruction of the composite due to a dangerous defect is accompanied by the emission of low-and high-frequency acoustic emission (100-130 Hz, 3.0-6.0 kHz); while the accumulation of defects in the material in the presence of a growing crack, acoustic emission is characterized by a gap frequencies from 2.2 to 3.0 kHz.