Hi guxin1985,
To tag onto this thread, you can absolutely shelter some of the capital gain with the 121 (primary home) exclusion since that was initially your home before you began renting it.
One other factor to consider is that for the time it was rented, you would have claimed the rental income, as well as rental expenses and depreciation on the home. When selling a rental property, depreciation is recaptured (at ordinary income rates, up to a ceiling of 25%) and this is treated separately from the rest of the capital gain.
For example: you bought the house for $300k and sold for $450k. You also took $10k of deprecation during the 2 years of rental. Your basis would be reduced to $290k, thus a gain of $160k. $150k of this gain may be excludable from the exclusion mentioned above, but the $10k attributable to depreciation is treated totally separately and not excludable.
https://www.journalofaccountancy.com/issues/2002/oct/thehomesalegainexclusion.html
