The invention discloses heat-insulating glass used for an oven. The heat-insulating glass comprises a glass substrate, a heat insulating layer and a protective layer; the glass substrate has an inner surface and an outer surface, the inner surface and/or the outer surface are/is provided with the heat insulating layer, the heat insulating layer is composed of silver, the protective layer is arranged on the heat insulating layer and used for preventing the heat insulating layer from being oxidized, and the protective layer is composed of silicone oil. The heat-insulating glass used for the oven takes advantage of the good heat insulating effect of silver, a silver layer serves as the heat insulating layer, the heat insulating effect of the heat-insulating glass is thus largely improved, when the heat-insulating glass is applied to the oven, the heat dissipating capacity and energy consumption of the oven are thus small, due to the high temperature resistance and protective performance of a silicone oil layer, the silver layer is prevented from being oxidized, at the same time, the transparency of the heat-insulating glass is not affected because the silicone oil layer has transparency, and the working stake of the oven can be observed through the heat-insulating glass. The heat-insulating glass used for the oven is simple in preparation process and low in cost. The invention further provides a preparation method of the heat-insulating glass used for the oven.