The post-construction settlement of road constructed on soft ground is significant and widespread. The current international roughness index（IRI） subjects some limitations. Hence，based on the driving comfortableness, this study proposed an assessment method for driving quality of roads on soft ground. Firstly，the influences of fitting methods and the distance of fitting points on the vehicle vibration acceleration were evaluated by five-degree 1/2 vehicle-road interaction model. The weighted root mean square of vehicle acceleration was thus obtained. Secondly, based upon the standard for vibration comfortableness（ISO2631），the equations for DCI and RQI for assessing the comfortableness of driver and passenger were developed. Finally, on the basis of two scenarios of soft ground and non-soft ground, the evaluation results calculated from the methods in this study and IRI were compared. The results demonstrate that, in the non-soft ground, the results are similar. In contrast, the results in soft ground are quite different, and the methods proposed in this study are more in line with the engineers′ visual sense.