The reform of treasury cash management is an important part of the construction of modern treasury system in China. The main task of deepening the reform is to establish the management system of the target of the cash balance in the treasury account. The key step is to determine the reasonable scale of the cash balance in the treasury account using scientific methods. In this paper, we analyse the Baumol model and MillerOrr model which are most commonly used currently, and propose using the Value at Risk (VaR) model in financial risk management to calculate the target of the cash balance according to practical situation. We use the net outflow data of Chinas central treasury in 20122017 to calculate the target of the cash balance in the central treasury account，and find that the number should be 120 billion yuan. At last，we put forward some policy suggestions for establishing the management system of the target of the cash balance in the treasury account.

国库现金管理改革是我国现代财政国库制度建设的重要内容。当前深化改革的主要任务是建立财政库底目标余额管理制度，关键是要采用科学的方法测定库底目标余额的合理规模。本文对目前常用的Baumol模型、MillerOrr模型进行了分析，结合实际提出使用金融风险管理中的在险价值（VaR）模型，利用2012—2017年我国中央国库日度净流出数据，对中央国库库底目标余额进行了实际测算,发现中央财政库底目标余额的合理规模为1 200亿元。本文同时提出了建立库底目标余额管理制度的有关政策建议。