Interaction between the interplanetary magnetic field and the earth's geomagnetic field at the dayside magnetopause is studied by a global two-dimensional incompressible MHD simulation. It is found that for a large magnetic Reynolds number (Rm≥400), the multiple X line reconnection (MXR) becomes the major dayside reconnection process, while for a small magnetic Reynolds number (Rm≤100), the classical single X line reconnection takes place. Since the magnetic Reynolds number at the dayside magnetopause is probably very high (Rm>103), it may be suggested that MXR will dominate the dayside reconnection pattern. As a result of the MXR process, magnetic islands are formed on the dayside magnetopause surface. The dependence of the dayside reconnection geometry of the solar wind Alfv¿n Mach number is also examined. ¿ American Geophysical Union 1988