The tsunami-generated magnetic field on seafloor was found to be a powerful tool for the tsunami early warning. Using the magnetic field, it is possible to detect the propagation of tsunamis and to estimate their wave height prior to their actual arrivals because it arrives earlier than the tsunami sea level change and very sensitive to it. However, these correlations have never been studied by the direct comparison between the observed tsunami magnetic field and sea level change. This study aims at the correlation between the tsunami magnetic field and sea level change using the observed data and the three-dimensional (3-D) simulation of the 2009 Samoa and 2010 Chile earthquake tsunamis. The comparison of the observed tsunami magnetic field and observed sea level change illustrated that the vertical component of tsunami magnetic field, Bz, has a phase lead to the sea level change. Combined with the 3-D simulation results, the initial rise in observed tsunami Bh which also arrives earlier than the tsunami sea level change was confirmed. We further examined the precision of conversion of the tsunami magnetic field to the sea level change. The results suggest that the converted tsunami sea levels have as high precision as the differential pressure gauge data. However, our simulation was unable to reproduce the observation well, because of the inaccurate tsunami source models. It, therefore, is necessary that the very precise sea level changes converted from the observed tsunami magnetic field should be used in constructing new tsunami source models.