By the conventional pulsed electroacoustic (PEA) method, only one-dimensional distribution of the average charge over a whole area parallel to the two electrodes can be observed. Therefore, we have developed a new PEA system capable of measuring three-dimensional space charge distribution. Using this system, we measured the charge distribution in glass/epoxy composites made of lattice woven glass fibers and epoxy resin. It has become clear that the space charge accumulation depends on the internal structure of the composite. There appear repetitious positions where a high charge density is observed on the same lateral cross section along the vertical direction in the composite. Such positions agree with the inter-sections of the glass fibers. These results clearly show that mismatch of the ratio of the conductivity and permittivity between the two composite materials is responsible for the observed space charge.