As an important electrical connector, the reliability of spring electrical connection directly affects the electrical performance of the device. It is important to study the regularity and influencing factors of spring electrical connection for improving equipment performance and saving cost. In this paper, through software simulation and experimental measurements, the rule is tested that the contact resistance decreases with the decrease of the resistivity of the contact metal surface material and decreases with the increase of the applied force when the electrical connection parts represented by the spring are under weak external force(<2N). Through the analysis and calculation of mechanical contact theory, it is verified that the contact resistance is affected by the resistivity and external force of the material. The mechanism of contact resistance of the projectile is clearly explained, and the relationship between contact resistance of the projectile and different contact interfaces can be more accurately judged.