To understand the bursting behaviour of microquasars, we performed time evolution of luminous accretion disks and the spectrum evolution, taking into account the inverse Compton scattering, gravitational redshift, etc. The spectra during the burst became a factor of 2-3 harder as the mass accretion rate increases, due to the inverse Compton process inside the disk. This trend is roughly consistent with the observational properties such as burst duration, luminosity, and maximum temperature of microquasar GRS1915+105.