A bone cement injection device includes an outer barrel including a side slot； an injection unit movably received in the outer barrel and including an inner tube that defines a first hollow section therein and an outer tube that defmes, in combination with the inner tube, a second hollow section therebetween and includes a guide tube mounted to the outer tube to be movably received in the side slot and in communication with the second hollow section； and a pusher unit movably received in the first hollow section and positioned against a bottom end of the outer barrel. Bone cement is filled in the first hollow section and is driven by the pusher unit into a patient's bone. An air compressor is used in combination with the guide tube to induce a pressure difference between inside and outside of the bone to help injection the bone cement into the bone.
