网络搜索学习了一下，仅供参考。大概相当于公司给员工发股票奖金，一部分卖了预交收入税，净额股票存托管，未来卖了差价算资本利得税。
For example,
Grant date: $40,000 for 4 years vesting. Generally no tax implications.
Vesting date of the 1st year : Vested stock value $10,000 = $25 per share x 400 shares - $25x 100 shares ( to withhold and pay taxes ) = Net $25 x 300 shares = $7,500 deposited in Fidelity or ETrade and become cost basis. $10,000 is shown in W-2 as ordinary income and $2,500 as withholding taxes.
Selling date: ($60 selling price - $25 cost ) x 300 shares = Capital Gain shown on form 1099-B
