Liang,
Even though you set Reservation/PR in order type dependent parameters as 2 when planned order to production order converted in CRTD status it self it creates the PR and Reservation and This is standard behavior of the system Please refer SAP note 1567876 - Planned order conversion: MRP relevance.
You have to change the message type for the system message C2 280 to change this behavior as described in Note 569984.
BR
KK