Electromagnetic interference (EMI) for low-temperature detectors is a serious concern in many missions. We investigate the EMI caused by the spacecraft components to the x-ray microcalorimeter of the Resolve instrument onboard the x-ray imaging and spectroscopy mission, which is currently under development by an international collaboration and is planned to be launched in 2023. We focus on the EMI from (a) the low-frequency magnetic field generated by the magnetic torquers (MTQ) used for the spacecraft attitude control and (b) the radio-frequency (RF) electromagnetic field generated by the S and X band antennas used for communication between the spacecraft and the ground stations. We executed a series of ground tests both at the instrument and spacecraft levels using the flight-model hardware in 2021–2022 in a JAXA facility in Tsukuba. We also conducted electromagnetic simulations partially using the Fugaku high-performance computing facility. The MTQs were found to couple with the microcalorimeter, which we speculate through pick-ups of low-frequency magnetic field and further capacitive coupling. There is no evidence that the resultant energy resolution degradation is beyond the current allocation of noise budget. The RF communication system was found to leave no significant effect. We present the result of the tests and simulation in this article.