The utility model discloses a device for improving the pouring compactness of the top of a partition wall in a double-arch tunnel. The device comprises a mid-partition vault end template, an exhaust pipe, a grouting pipe, a pipe bottom protection device and a PE breathable film, the mid-partition vault end formwork is arranged at the end of a mid-partition vault. wherein a grouting hole and an exhaust hole are formed in the middle partition wall, the exhaust pipe is pre-buried in the exhaust hole, the grouting pipe is inserted into the grouting hole reserved in the arch crown end template of the middle partition wall, a pipe bottom protection device is arranged at the bottom of the grouting pipe, and a PE breathable film is pasted to the top of the middle partition wall and can exhaust airat the far end of the grouting hole. When the device is used, the operation is simple; the method comprises the following steps: filling a gap between a mid-partition wall body and a middle pilot tunnel primary support by spraying concrete; the grouting machine is used for grouting the top of the mid-partition wall, air at the far end of a grouting opening is exhausted through the PE breathable film, concrete is prevented from generating a cavity, and the device is easy to manufacture, convenient to operate, low in cost and capable of effectively improving the grouting compactness of the vault of the mid-partition wall of the multi-arch tunnel.