A near space atmospheric density detection method based on hypersonic reentry sphere was proposed with the aim of overcoming the shortages of current detection methods, such as the low accuracy, the high cost and the weak time-space conformity. The measurement error was analyzed according to the kinematic equation of reentry sphere. The results show that the atmospheric density below the height of 90 km can be detected with the accuracy level below 6%. The antenna placement scheme was determined by analyzing the 6-DOF (degree of freedom) motion model of the sphere with eccentric balancing weight and combining with the numerical simulation of aerodynamic heat. Numerical calculation of heat conduction along ballistic trajectory for the eccentric sphere with double radome was achieved and the thermal protection scheme was performed eventually to demonstrate the feasibility of this detection scheme. The proposed detection method of atmospheric density can provide a meaningful reference to the construction of highaccuracy nearspace atmospheric density.