The invention belongs to near space environment, atmospheric density measurement, and aerodynamic parameter identification devices, and specifically relates to an accompanying atmospheric density measuring device. The device comprises a frame. Sheet metal reinforcement is applied inside the frame, such that inner devices can be fixed. A power source, a three-way overload sensor, a central processing unit, and a GPS radar integral machine are sequentially fixedly arranged on an end of the frame. An antenna is sleeved on the frame, wherein a certain gap is preserved between the antenna and the GPS radar integral machine. The invention has the advantages that: as a means for following the flight path of a reentry vehicle and for carrying our density measurement, the accompanying atmospheric density measuring system is simple and reliable, and has low cost. With the accompanying atmospheric density measuring device, measuring demands of aerodynamic parameter identification can be satisfied. Also, the invention is designed independent from a reentry vehicle, such that the overall design difficulty of the reentry vehicle is not increased.