One kind of heat treatment machine for powder material was designed to use the metal screw impellor inside the sterilization chamber as the heating component connected to high frequency electricity. As strong magnetic field was generated during the process, the accuracy of temperature at critical control point (CCP) of the material measured by platinum resistor would be influenced, and this entailed the electromagnetic shielding (EM shielding). Based on both theoretical analysis and virtual simulation, our research was intended to design the shielding device. The relationships between the shielding effectiveness and the relative permeability, relative conductivity and thickness of different materials were analyzed. After narrowed down to several kinds of materials with various thickness, the shielding effectiveness of these materials was calculated by virtual simulation. It was found that Mn-Zn ferrite would be the proper shielding material for platinum resistor and the effectiveness of a 3 mm thick Mn-Zn ferrite cylinder shield could be higher than 40 dB. The shielding effect of this device prototype was proved to be acceptable in this study.