Can anyone please tell me in detail what is difference between " Dealing Desk or Non-Dealing Desk broker "
Thanks
Dealing desks are intermediaries, a middleman for simplicities sake. They act between the bank and the individual traders in placing trades, & thus have room to manage the trade. Non-Dealing Desk brokers on the other hand have no intermediaries and place your trades direct with the banks. As a result most times Non-Dealing Desk brokers offer much better spreads.
But if you are looking to choose a broker just on those grounds, I’d suggest you to look at other aspects like customer support and the benefits they provide. Also, always make sure you choose a reputable and sound broker. Use the comparison tool on babypips, they have quite good information there.
Hope that helps 
A dealing desk can make a market. This means they can determine what liquidity to offer traders, determine the prices at which you can buy and sell, and take the other side of a traders position. They make a market in which you can trade. They then manage the risk they are taking on by providing this market.
A no dealing desk broker is acting as an agency providing you access to multiple market makers passing your orders to those market makers for execution. So they are not taking on the risk of making the market. As a part of this they do not control the liquidity being provided or the pricing you see on the platform. The liquidity and pricing is dependent on what the market makers are offering.
In more detail. it’s means the DD is actually the method for market maker(only). and can make a market means the MM broker can sell/buy at the price not provide by bank?
can explain in more pratical.
as the above explain:
Trader>> deal with MM broker.
and MM broker deal with BANK/MM broker.
there are 2 action. well the action between Trader and MM broker it not influnce the action between MM broker and BANK/MM broker.
right? it like trading company.
company ABC get product from factory at price $30, and company ABC can sell it at $31 or $29.
as you were explained before - there is some technical difference between those types of traders, but from my practice I can tell you, that for trader there is no big difference (maybe except of those who use scalping strategies)