The invention relates to a method for forming a super thick insulating layer in a through-silicon via through thermal oxidation, aiming at the problem that a thicker silicon oxide insulating layer is difficult to form since the oxidation speed is reduced greatly after the thickness of the oxide layer exceeds 1 micron in a process of producing the silicon dioxide insulating layer by a thermal oxidation method. According to the method, a hole (101) and an annular silicon region (20) are formed in a substrate (10); the annular silicon region (20) is distributed in the shape of a concentric circle around the hole (101); the side wall of the through-silicon via is etched to be annular; and then the annular silicon is oxidized to obtain the silicon oxide insulating layer. Considering the volume change proportion of silicon oxide formed in the through-silicon via, a periodic ring structure is formed through deep etching at a certain space, and the silicon ring is oxidized by using a thermal oxidation method to obtain the thickness of the required oxide layer. According to the method, the compact silicon oxide insulating layer with unlimited and controllable thickness can be obtained.