In this paper we present a modified real-coded lattice gas (RLG) model in which the floor field is introduced. The floor field is calculated on finer lattices in order to determine the pedestrians' direction accurately. Thus, the pedestrian's motion has many more degrees of freedom compared with existing discrete models. Furthermore, the walking speed is determined by the available space ahead of the pedestrians in a multi-step way. Therefore, the model can precisely describe the pedestrians' motion. Then, we calibrate model parameters by comparing with the existing measured data. Finally, we employ this model to investigate normal evacuation from a room. The conclusions are as follows: 1) In the single-exit room, for a given exit width larger than 0.6 m, the average specific flow increases with the initial number of pedestrians. For a given initial number of pedestrians, the specific flow increases first and then decreases when the width of the exit increases. 2) The evacuation time of the two-exit room is less than that of the single-exit room only when the total width is greater than 1.6 m.