Truncating a table with a foreign key constraint - SQL Server
The documentation for TRUNCATE TABLE (Transact-SQL) is fairly clear on this topic.  

Referencing the Restrictions:


  You cannot use TRUNCATE TABLE on tables that:
  
  Are referenced by a FOREIGN KEY constraint. (You can truncate a table
  that has a foreign key that references itself.)




Regarding your comment


  I don't want this operation to be logged in transaction log that's why
  I wanted to use truncate instead of delete operation.


The TRUNCATE TABLE command is fully logged, just not at the row level.  Within a transaction, it can be rolled back.

Referencing the REMARKS section of the documentation.


  Less transaction log space is used.
  
  The DELETE statement removes rows one at a time and records an entry
  in the transaction log for each deleted row. TRUNCATE TABLE removes
  the data by deallocating the data pages used to store the table data
  and records only the page deallocations in the transaction log.