when I give Limit Value it seems burst only occurs in the beginning of download and then the connection speed drops to Max-Limit value not to Limit value. And, when I remove Limit value it seems it is normal. So which value could be effective after burst-threshold?
Make sure you understand the difference between limit-at, max-limit, burt-time, burst-limit, and burst-threshold. It sounds like you may have them confused.
You can read here.
http://wiki.mikrotik.com/wiki/Manual:Queue#HTB_Properties