Abstract: Conventional electromagnetic logging while drilling is an important method for evaluating stratigraphic fluids, but it does not have azimuth characteristics. In this paper, a new modular structure of electromagnetic logging instrument while drilling is proposed to make it have good azimuth detection characteristics. In order to accurately understand the influence of modular electromagnetic logging instrument structure while drilling on the measured voltage signal, a three-dimensional model was established using the finite element method, and explored the influence laws of various instrument structures. The results show that with the increase of resistivity of drill collar and antenna slot filling, the received voltage signal has a sudden interval, which is closely related to the frequency and geometric size of the instrument. The resistivity of the cover material has a great influence on the strength of the received signal, and the cover plate should be selected with a slightly lower resistivity than the metal. The measurement signal increases with the increase of resistivity of the sensor body, so the sensor body should be selected as a non-metallic material. When the resistivity of the instrument structure such as drill collar and filler is low, the received voltage signal has obvious attenuation, and its influence can be ignored when the resistivity of the filler is high. After the deduction of the influence of the instrument structure, the magnetic flux in the coil decreases, resulting in the instrument signal being smaller than the instrument signal before the deduction. This study can provide a theoretical basis for the actual instrument design.