The present invention provides a siloxane rubber sponge having high opening ratio, which has homogeneous microporous structure prepared by normal pressure heat air vulcanization (HAV) without influence of crosslinking velocity of rubber and generation velocity of foaming gas. A siloxane rubber foam of 20% or higher opening ratio is obtained by foaming and vulcanizing a siloxane rubber compound, which contains: (A) 100 weight share raw material which is obtained by heat treatment to mixture of reinforcing silicon dioxide and organopolysiloxane which contains at least two alkenyls connecting to silicon atom in each molecule and is of formula (I): R<1>aSiO(4-a)/2, wherein, R<1> is same or different non-substituted or substituted monovalent hydrocarbon radical, and a is in the range of 1.95-2.04; (B) 0.5-50 weight share organic blowing agent; (C) adequate vulcanizing agent; and (D) 0.1-20 weight share wet silicon dioxide.