Abstract: In this review, I briefly summarize the scientific objects of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) program and the major findings so far on Mars internal structure. The focus is on InSight's SEIS (Seismic Experiment for Internal Structure) project. Based on the observation up to date, it appears that SEIS is able to provide relatively precise depth profile of the physical properties of the regolith and bedrock underneath the InSight landing site. It is also able to provide certain constraints on Mars crust at the local to regional range. It may also place some constraints on properties of Martian upper mantle. However, it has been unable to provide meaningful constraints on the property of the core so far. The main reason is the lack of strong sources (large Marsquake or impact) that can generate seismic waves propagating in the entire planet.