The temperature-dependent spatial structure of perovskite oxide La0.55Ca0.45MnO3 has been checked by X-ray diffraction (XRD) and Rietveld method was employed to refine the XRD data. It was found that with the decrease of temperature, almost all of the diffraction peaks were split; each peak was divided from single peak at high temperature into two peaks at low temperature, indicating the appearance of a crystalline structural phase transition. Corresponding to the structural phase transition, magnetization measurements also revealed a magnetic transition from ferromagnetism to antiferromagnetism. With the Rietica analysis of the XRD data of the compound, plots of the electronic density distribution of La0.55Ca0.45MnO3 were made. Sharp difference in the distributions above and below the transition temperature was clearly shown. Taking the magnetism of the compound into consideration, the structural phase transition was analyzed and the sharp difference of the electronic density distribution was qualitatively explained.