Experimental study was carried out on the ion thruster plume thermal effect within the scope of thruster exit radius of 500, 700 mm and 900 mm, the angle of 0°-15° (assuming the thruster exit plane as the center of the circle, thruster exit axis as 0°) with the help of the heat flux sensor. PIC-DSMC (particle in cell direct simulation of Monte Carlo) algorithm was used to simulate the experimental conditions under different adaptation coefficients. The results showed that the adaptation coefficient of keV energy Xe particles to the surface (copper) of the heat flow sensor was close to 1.