Same physical quantity measures the different order of same physical quantity. The value of any given physical quantity may vary over a wide range, so different units of same physical quantity are required.
e.g., length or distance can be measured in different way such as the length of a pen can be easily measured in $\mathrm{cm}$, the length of a tree can be measured in metres, the distance between two cities can be measured in kilometres and distance between two heavenly bodies can be measured in light year. So we have the different units of same physical quantity.