In order to study the influence of structural parameters on characteristics of fragments from warheads with a composite charge， AUTODYN-3D finite element calculation software was used. Next the propagation of detonation waves and shell breaking process of warheads were compared and analyzed， under the central single-point initiation and the internal and external simultaneous initiation. Then the influence of shell thicknesses and central charge diameters on the average mass and velocity of fragments from warheads was obtained. The calculation results show that， with the increase of shell thicknesses or the decrease of central charge diameters， the average mass of fragments under single-point initiation increases more times than that under internal and external simultaneous initiation， and the difference in power output of warheads between those two initiation modes becomes more significant. The static explosion test results show that the average velocity of fragments， shock wave overpressure， and the number of witness target holes under internal and external simultaneous initiation increase 27.1%， 31.4%， and 39.3%， respectively， compared with those under single initiation. The test results are in good agreement with the calculation results.