The resistivity of magnetic samples at the micro-and nanoscale is affected by various factors such as temperature, size, and applied magnetic field. The traditional two-wire method to measure the sample resistance is easily affected by external interference, and the presence of contact resistance will lead to the measurement results not being precise enough, which affects the experimental results. In this paper, the four-point probes method is used to study the resistance characteristics of magnetic microwire samples. Firstly, two different sizes of nickel microwire are prepared based on photolithographic process, and at the same time, a measurement system that can accurately control the temperature and the magnetic field is used to study the effects of the ambient temperature and the external magnetic field on the resistance of the samples of different sizes. The experimental results show that the resistance value of the nickel microwire almost does not change with the temperature in the low-temperature region below -250℃, and then increases approximately linearly with the increase of the temperature; at room temperature, the resistance value of the nickel microwire increases with the increase of the strength of the external magnetic field, and the resistance value of the samples is basically stable after the magnetic field strength reaches 2 000 Gauss. The article explains the temperature effect, size effect, and magnetoresistance effect of magnetic microwire resistance from the microscopic electron transport perspective.