A method for determining the residual stress through the deformation of a witness sample during pneumatic blasting of gas turbine engine parts with microbeads is proposed. During the study, the processing modes and the diameter of the microbeads were changed. It is shown that with an increase in the diameter of the micro-ball from 0.3 mm to 0.7 mm, the deformation of the samples increased by 2 times, and with an increase in the speed of their movement from 70 m/s to 90 m/s by 50 %. The mechanism of formation of residual stresses and deformations of the treated surface of the witness sample is proposed.