The utility model discloses a building expansion joint waterproof construction, include: the cushion, its fixed mounting is on the expansion joint, first waterproof member, its first connecting portion that have a water drainage tank and U -shaped, the waterproof member of second, it has the 2nd water drainage tank and is second connecting portion of U -shaped, the structure of the waterproof member of this second is symmetrical with the structure of first waterproof member, first waterproof member and the waterproof member of second through first connecting portion and second connecting portion looks lock joint and fixed mounting on the cushion, behind these first connecting portion and the second connecting portion looks lock joint, has the clearance of reservation between it. The utility model discloses the seepage problems that the factor leaded to such as waterproof ageing, shrink, fracture, basic sedimentation coefficient nonconformity can be solved effectively, expansion joint this technological problem of antiseep in the space such as bathroom is solved to can avoid the later stage to leak effectively and maintain a series of problems such as inconvenient, effectively reduce the later maintenance maintenance cost, guarantee the waterproof quality of construction.