Dear yuyu li,
depend on your exact case, I would suggest you 2 approaches.
1 - I if you need just energy deposition scoring per particle. There is specific Fluka instrument created exectly for this use case - DETECT card. Which scores energy deposition per event
https://indico.cern.ch/event/656336/contributions/2729627/attachments/1552510/2439699/Scoring.pdf, page 4,
and also forum thread How to use the DETECT card
2 If you want to proceed to scoring several parameters, e.g. deposited charge of secondary electrons, I use a trick of running arrays of USRBDX and USRBIN detectors with an exaggerated number of runs, and then processing result with an external script.
Best regards,
Illia