Development of Fast Imaging Solar Spectrograph (FISS) is a collaborative work between Seoul National University (SNU) and Korean Astronomy and Space Science Institute (KASI). FISS is an imaging spectrograph which adopts Echelle disperser with field-scanning method. Single paraboloid mirror is used as both collimator and imager, which can be regarded as quasi-Littrow configuration. Dispersed beams are collected by two CCD cameras that will be preceded by order-selecting narrowband filters, so that images of dual spectral bands can be acquired simultaneously. According to the orientation of the grating, we can get various kinds of dual-band combination. With this dual-band feature, we can distinguish thermal and non-thermal contribution to the spectral line profiles.