As a developer，I want to use the interface to search this information: which can get the amount which nominator has been rewarded at every era and staking?
Probably what you are looking for is to inspect the
Rewarded event and find the one that corresponds to your nominator of choice. Some useful links to docs/tools:
https://paritytech.github.io/substrate/master/pallet_staking/enum.Event.html#variant.Rewarded https://polkadot.js.org/docs/substrate/events#rewardedaccountid32-u128 https://polkadot.subscan.io/event?address=&module=staking&event=rewarded&startDate=&endDate=&startBlock=&endBlock=&timeType=date&version=9281