we normally used same material in the assembly . so i want to change the pro e default density value .......
I think you mean this?
Answered with a tutorial: https://grabcad.com/tutorials/how-to-change-default-density-value-in-pro-e
I don't think it is possible in assembly; but you can modify material properties of a part.
Go to File--Properties--Assign material to your part--Change the units if you want--In front of Mass Properties you will find a 'i' symbol--click on that symbol and you will find a report generated.
In this report you can find density of a part.