How to calculate earned value based on duration in P6 (Earned days or weeks)

Mohamed,

It is quite easy. You simply apply a resource to each activity, with the default units per time period (simplest if this is 1) This can be done in one pass with the multiple-assign function. 

Earned value can only come from resources in P6, but if the budget quantity is the same as the duration, then earned value becomes a function of Duration % complete.

Issues:

P6 only earns value from a baseline.  Be careful. 

If there are "real" resources in the plan, you will need to price these at zero in order for them not to be included in the earned value calculations.