What is the relationship between the atherosclerosis and hypertension?

Atherosclerosis is the hardening or thickening of the blood vessel walls. The maintenance of blood pressure is dependent on the distensibility of vessels. So if a vessel can't distend/widen itself to accomodate more blood, you have increased pressures inside of that vessel, leading to hypertension.

Ultimately, atherosclerosis leads to hypertension.

blood flow is related by the following Darcy's law. (if you are an physicist/engineer, it is pretty much the same as ohm's law
q=p/r

flow is q, p is pressure, r is resistance

in atherosclerosis, there are hard plaques that form inside the vessel, making them very stiff and harder to stretch, so the resistance(the 'r') will increase. bcos they are indirectly proportional, the flow will decrease;pressure needed to generate the same amount of flow will have to INCREASE in order to maintain the SAME flow

eventually this compensatory mechanism can wear our and lead to main other condtions like heart attack, stroke, kidney problems, eye problems, diabetes...

Similar to what fire4830 has said, atherosclerosis is the thickening of blood vessel walls. This then causes the artery to become less flexible when more blood flows through. This creates a pressure on the artery, known as blood pressure. And since hypertension is blood pressure, atherosclerosis leads to high blood pressure.