I have a custom date/Time field in salesforce for a object and i am trying insert values for that field through the data loader.I have used yyyy:mm:dd hh:mm:ss date format in excell. User time zone and company default time zones are same.But when i insert data to that field it's showing date as data as given date -1 day.This is the sample data 
But in salesforce it is stored as 
and 
What should i do to store the exact date from excell?
You want to format it as:
yyyy-mm-ddThh:mm:ssZ
Where you can just make hh:mm:ss be 00:00:00.
e.g. 2016-01-18T00:00:00Z
Some versions of Excel don't have date-time formats available in the standard pick lists, but you can just enter a custom format string such as yyyy-mm-dd hh:mm:ss by:
Right click -> Format Cells Number tab Choose Category Custom Enter your custom format string into the "Type" field This works on my Excel 2010
Two things about loading date types:
Data loader ignores the HH:MM:SS portion of Date types, so you can just write it as YYYY-MM-DD. Reserve the HH:MM:SS for Datetime types.
Data loader interprets all dates as GMT. When you look at it in the UI, you are looking at the local time which is MT(GMT-6).
Date '2016-01-18' in the CSV, after the load it becomes '01/17/2016 18:00:00' in the UI.
Data import wizard requires Datetime to be in "mm/dd/yyyy H:MM AM/PM" format.
Also make sure that timezone set for your org is same as your machine's.
