Loop ramp is a kind of commonly used interchange ramp form, at the same time it is also a accident prone section with difficult driving condition because it is a curved- slope combination section. In order to clarify the lateral acceleration characteristics on loop ramp, three complete clover leaf interchanges and one partial clover leaf interchange in Chongqing jurisdiction were selected as the research object, and the real vehicle driving experiment carried out, The continuous lateral acceleration of running cars under natural driving conditions were collected, and the amplitude level, changing trend and patterns of lateral acceleration for loop ramp are defined, and the main conclusions are as follows: There are significant differences in the amplitude and appearance morphology of lateral acceleration curves of different drivers, but they can be classified. Ride comfort level in lateral direction of loop ramps of three completely clover leaf interchanges are general, and comfort level for loop ramp of one partial clover leaf-shaped interchange is poor (uncomfortable). The patterns of lateral acceleration for loop ramps can be divided into seven kinds, five kinds of which are the three-stage patterns, one is two-stage and the other one pattern is four stage. The pattern with largest proportion behaves: the value of lateral acceleration is still monotonically rising in the middle stage of the loop ramp. Increasing the length of spiral curve can reduce growth rate of lateral acceleration when drivers entering/departing the loop ramps.