Abstract: In the study of atmospheric inversion based on radio occultation, the residual ionospheric errors have great influence on the accuracy and the second order errors are not ignorable. In this paper, MSIS90 atmospheric model, 3D NeUoG ionospheric model and IGRF11 geomagnetic model are all collected, and 3D ray tracing method was used to simulate the changes of the second order residual ionospheric errors in radio occultation. Under different solar activities, local time, azimuth, the second order errors were analyzed, especially for its global distribution. The results show that second order errors are usually in sub-centimeter level, but up to centimeter level under higher solar activity or in middle and low latitudes at 0° or 180° azimuth, and illustrate the structure of “three-peak” in globe. Therefore, in the occultation data process, the ionospheric monitoring must be strengthened and second order ionospheric errors must be eliminated effectively.