The invention discloses an auxiliary device for processing of an oblique oil hole, which comprises an on-line supporting frame, drilling tool supporting sleeves, drilling tools, returning springs and a drilling pressing arm. The drilling tool supporting sleeves are slantingly and fixedly arranged on the on-line supporting frame; the on-line supporting frame is provided with through holes; the through holes are communicated with the insides of the drilling tool supporting sleeves; the drilling tools are arranged in the drilling tool supporting sleeves in a sliding manner; the returning springs connected between the drilling tools and the drilling tool supporting sleeves; a linkage mechanism is arranged between the drilling tools and the drilling pressing arm; the drilling pressing arm is rotationally connected with the on-line supporting frame by a rotating shaft; and the on-line supporting frame is also provided with a workpiece clamping mechanism. The auxiliary device for processing of the oblique oil hole is low in cost, has a simple structure, occupies a small space, is easy to load on line, can be integrated into an existing production line to carry out online drilling processing on an engine cylinder head, avoids a product being moved around, reduces twists and turns and enables drilling processing to be efficient and labor-saving.