when i isuue the command:show ip eigrp neighbor;in the Q Cont field,when the value of this filed its 15,is there any problem,if so what is the reason of the problem.
The Q count field is the number of EIGRP packets (updates, replies and queries) that the router is waiting to send. If you have a Q cnt greater than 0 it means your router is not receiving acknowledgements for the packets it is sending.
This could be transitory due to a congested link etc. What is more important is
Do you see the Q cnt going down at all ?
Is there a figure in the SRTT field ?
And are you seeing the neighborship with the other router going down at all.
If you are seeing any of these symptoms you need to look at link itself between these routers.