What causes swelling and hardening like a part of vein in the penis ?

It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some tests. A vein with blood clot in it, thrombosis could create the situation you described. It would be prudent to see a doctor. Wish you good health!

The vascular structure of the penis is complex and robust, but not superman. Usually a hardening of a vessel is cause by trauma to a vein, which then forms a blood clot or thrombus within. This will usually heal by itself without further trauma. If it progresses or becomes painful, then go to see your doctor.