Abstract: A laboratory simulation is made to show the effects of microgravity on the cellular shape and structure of rat's cardiac muscle. The cell's cultural system is put into a simulated microgravity environment. It is found that cellular morphology changes from slim to round in optical microscope and cytoskeloton changes from columnar morphology to radial morphology through marked Actin in fluorescence microscopy. Cellular area of cardiac muscles becomes significandy decreased by 40% and cellular long-short axes ratio decreased by 70% through micromeasurement.