Quote from baidu2005:
...EUR, USD have higher interest than that of CHF.
Not necessarily, in the real world of retail forex... As the name suggests, when it comes to interest debits and credits for your currency trades, you are paying "retail", not "wholesale" such as the local, currency-specific LIBOR rate.
At IB, that retail v. wholesale difference comes to 2%, for all the majors, when trade size is under USD 100K. That's 1.5% spread over a short currency local LIBOR for interest debits, 0.5% spread under a long currency local LIBOR for credits, total 2%. That alone easily explains your EUR/CHF net debit / negative interest. (Wholesale LIBOR spread is about 3.32% - 1.84% = 1.48% < 2%, going by IB's published benchmark rates at the 2nd link below.)
This issue was discussed in some detail a few months ago, within the context of a long-term dollar-yen reverse carry trade, futures v. spot:
http://www.elitetrader.com/vb/showthread.php?s=&threadid=66505
In addition, uniquely to IB, you don't get any credit under USD 10K or the equivalent in other currencies. This exclusion drives down your effective credit rate sharply, for smaller balances. In combination with the 2% factor above, this might explain your USD/CHF net debit as well, despite the seemingly untouchable LIBOR spread, currently about 5.29% - 1.84% = 3.45%.
Have you looked at this page? It's fairly self-explanatory.
http://www.interactivebrokers.com/en/accounts/fees/interest.php?ib_entity=llc#shortCredit