SOLVED
It requires 10 days 24-hour to sync with fast sync. It first download block, more or less 3.7 million, then start downloading states, certainly more than 40 million, probably more than 50 million.
Start sync with geth --testnet --syncmode "fast" --rpc --rpcapi db,eth,net,web3,personal.
You can check the sync status attaching to the console: geth attach http://localhost:8545 and typing eth.syncing. false means the sync process is ended and the blockchain is ready to use.