It is time to file Self-Assessment for the taxpayers whose annual income exceed RMB120,000 in 2017. 31st March, 2018 is the last day to do that. 

There are 2 ways to file it:

1- Downlaod the system from tax bureau website to computers: http://shiju.tax861.gov.cn/nsfw/bstd.htm - 个人所得税12万自行申报

2 - Use cell phone APP: 支付宝 Alipay. Search for 北京地税. Then register for 12万申报. 

The system will show Gross income, taxable income and tax paid automatically. Amend or confirm the data, then submit it. 

Follow the instruction will done that.