Abstract: Based on the investment idea of intrinsic value, it discusses the strategy for longterm investment in stocks by the method of stochastic process. The premise for a successful longterm investment is to choose a growing company. The concept of stock's reasonable valuation was defined to reflect the stocks intrinsic value. The key to long-term investment is to track the dynamic changes of the company's growth and the stock's reasonable valuation in real-time. In order to avoid market risks and to get profits steadily, it proposes and proves the strategy for stock purchase and dynamic stock ownership, based on the benchmark for stocks'reasonable valuation.

Key words: intrinsic value; reasonable valuation; company's growth; strategy for long-term investment