It is generally believed that Type Ia supernovae are thermonuclear explosions of carbon-oxygen white dwarfs (WDs). However, there is currently no consensus regarding the events leading to the explosion. A binary WD (WD-WD) merger is a possible progenitor of Type Ia supernovae. Space-based gravitational wave (GW) detectors with great sensitivity in the decihertz range like DECIGO can observe WD-WD mergers directly. Therefore, access to the deci-Hz band of GWs would enable multi-messenger observations of Type Ia supernovae to constrain their progenitor and explosion mechanism. In this paper, we consider the event rate of WD-WD mergers and minimum detection range to observe one WD-WD merger per year, using nearby galaxy catalog and the relation between the Ia supernova and the host galaxy. Furthermore, we calculate the DECIGOs ability to localize WD-WD mergers and to determine the masses of binary mergers. We estimate that if the deci-Hz GW observatory can detect the GW whose amplitude is $hsim10^{-20}[rm Hz^{-1/2}]$ at 0.1 Hz, 1000 times higher than the detection limit of DECIGO. In fact, DECIGO is expected to detect WD-WD ($1M_{odot}-1M_{odot}$) mergers within $z=0.115$,corresponding to the detection rate of $sim20000,rm yr^{-1}$, and identify the host galaxy of WD-WD mergers for $sim8000$ WD-WDs only by the GW detection.
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