There are many anomalies beyond the explanation capacity of CAPM and APT. In their asset pricing models with heterogeneous agents, Miller and his successive researchers shed some lights on the effects of trading, but they only analyze the behavior of stock owners, neglecting the behavior of owners of risk-free assets(say government bonds). Without the assumption of short sale constraints and irrational behavior, we provide a new model with heterogeneous beliefs due to new information, by including effects of speculative behavior of both stock owners and bond owners. Significantly different to existing models, our asset pricing equation connects the asset price with the new information, turnover and relative quantity of the asset to the risk-free bond. Our model provides an explanation for the overvaluation and undervaluation of the asset price, and implies that an the relative quantity of stocks to bonds plays a key role in the evolution process of the stock price. In our model, overvaluation is not a negative and useless so-called price bubble, but the rewards to exploring uncertainty. Illustrated in the case of the rise and crash of the 90's internet boom, an effective policy is provided to ease the volatility of asset prices, that is, government should stabilize the quantity of the government bonds and relax the regulation of the financial market to facilitate the adjustment of the quantity of financial assets in the market.