What happens after disconnecting DC powered inductor?
voltage over an inductor is proportional to the di/dt .

Correct. Which also means that the di/dt is proportional to the voltage across the inductor.

I want to know what happens if I disconnect an inductor from a dc power suddenly. after disconnecting no current could pass through it . right ?

Before 'after disconnecting' we have the 'disconnecting' phase.
If the switch opens slowly, then as its resistance increases a little, the current through this resistance creates a voltage, which starts to ramp down the inductor current. The current may ramp down before the switch arcs. If the switch opens fast enough, current will still be flowing when it's open, and the voltage may rise high enough to induce an arc.
If we have some magic rapidly opening switch, the inductor current will still flow to somewhere. It flows into the stray capacitance of the inductor itself. The maximum voltage this capacitance will reach is given by the energy balance. The 0.5LI2 of energy originally stored in the inductor will become 0.5CV2 of energy stored in its capacitance, or an external capacitor, if one has been added to the circuit to limit the voltage rise, just like on the old style points ignition of a car.

so the voltage must tends to infinity or make a spark ?

There is always some stray capacitance, so it will never reach infinity. But it can get high enough to be embarassing, or to arc across switch contacts, or to break down semiconductor devices connected to it.