The magnetic reconnection environment around the dayside geomagnetopause under steady southward interplanetary magnetic field conditions is investigated using the in-situ observation by GEOTAIL satellite. We focus on the degrees of asymmetry in the plasma density, plasma temperature and the magnetic field strength between the both sides of the magnetopause, that is, the ratio of the value in the magnetosphere to that in the magnetosheath in order to build much more realistic initial condition in numerical simulation. GEOTAIL satellite repeatedly across the magnetopause during a single pass due to the oscillating of the magnetopause. The degrees of asymmetry varies even during a single pass. We suggest these variations in the degree of asymmetry is caused by the dawn-dusk asymmetry of magnetic field strength due to the Parker spiral of the interplanetary magnetic field. The degree of asymmetry in the magnetic field strength is less than 4 and more than 0.5. The smaller degrees (<1.0) are observed in the dusk side. In the numerical simulation of the asymmetric magnetic reconnection in the dayside magnetopause, we should set the constant temperature ratio ~ 20 in the initial condition.