As the current power grid system is upgrading to the smart grid, it becomes more vulnerable to security attacks on its communication subsystem such as the denial-of-service attack. Jamming, as a kind of denial-of service attack, can be applied to interfere the real-time communication in smart grid. In this paper, we analyze the scenario in which the attacker can jam a reduced number of signal channels carrying measurement information in order to manipulate the locational marginal price and create the opportunity for gaining profit, and the defender is able to guarantee a limited number of channels in information delivery. Based on the electricity marketing model, we propose a multiact dynamic game between the attacker and defender, in which the optimal strategies are taken by the two sides to maximize their own profits. We study the gaming process and discuss the prosperities of the outcome. Simulation results present the affect of jamming attack on the electricity prices and the gained profits of the two sides. Moreover, they confirm the optimality of the proposed scheme in pursuing profit.