Relationship between blood clot in leg and venous pressure?

Yes: Obstruction to venous flow, stagnation , slow flow state, inactivity will cause DVT ( deep vein thrombosis ) besides other systemic diseases that is the reason have to walk in long flights, and drives to prevent DVT and not to stay on the seat for hrs with out moving.

Yes, but...: ....It is not the most important factor. Many people have high venous pressures due to venous insufficiency, and while this may increase your risk of dvt, things like immobility, cancer, hormones, and smoking increase it much more.

Indirect: High venous pressure is often a sign of venous incompetence (valves not working). Often dilated veins and slower venous flow are associated with this, which may lead to more blood clots. Risk factors more closely associated with blood clots (dvt's) are immobility, trauma, hormones, cancer, hypercoagulability and previous dvt.