Wireless Access

What is the best distance between 2 access points AP175 that will be used with downtilt antennas in celling hight 12 meter?

Are you looking for spacing between APs for client coverage (ala what cell sizes you need)? If so, that will be dictated by your client requirements and what kinds of contiguous minimum SNR you will require, or what applications and bandwidth requirements you have. 

Customer signal about -65

2.4Ghz only or 5Ghz? Laptops only or phones and tablets? Wide open area with line of sight to the AP always, warehouses with tall/dense shelving, what kind of materials are stored on the shelves if so? Large industrial area? Are there any HVAC ducts above between the users and APs, etc?

My rough estimate is a 80-100m diameter of coverage with the ANT-90 at 15m height indoors within an industrial environment, with semi-clear line of sight, NOT containing any tall warehouse shelving, etc. That's my best guess. The more open and clear the environment, the larger the cell size coverage using the ANT-90 DT Omni (maybe to a diameter of 110-120m).

The client type will also dictate the Rx SNR at the client (tablets will see poorer SNR than laptops generally, rugedized handhelds are usually as bad or slightly worse than tablets, etc).

Cstomer have PCs with PCI cards support 802.11n and it is a steel factory and there is a lot of metal materials and hight of 10 meter  and thats will be our celling hight and we will use 2.4 GHZ so what is your recommendation for teh eight distance?

Originally you stated 12m height? I'm reticent to give an estimate based on your description. If your metal stacks are on shelving and they are 10m high within a 12m high ceiling, you would need to provide floor plans with the floor layouts to get any smarter recommendations. Otherwise I would go as lo as 20m diameter, as I get the feeling there's not much line of sight from where these workstations are and where the APs would be mounted,

Would need loads more details to give better planning data, from me anyway...