Many articles agreed that it is possible for speculators to manipulate stock prices. In this article, we give a dynamic model to show in detail how one type of the trade-based manipulation is realized in stock markets, especially in emerging stock markets, where manipulators have dominative information and fund over the uninformed investors. In our model, we assume that uniformed investors predict future price movement with their forecasting model, the number of uniformed investors who decide to buy stocks increases with fitting degree of the forecasting model for past price data and the model parameters. With these assumptions, manipulators take two-step strategy (pumping the price and selling stocks at higher prices), the pumping step aims to absorb uninformed investors' following by buying the stock by use of the forecasting model, and the selling step is to sell all the stock in higher prices by trying their best to control the supplies and continually attracting the uniformed investors’ following. We show that manipulators can realize their strategies and maximize their final wealth by controlling the strength of pumping and deciding the time length to sell out the stocks. Two numerical examples are also given.