Utilizing the muzzle voltage of the electromagnetic railgun, the contact resistance between the sliding armature and the copper rail surface during the launch process can be calculated to analyze the contact characteristics. However, the muzzle voltage signal contains a large amplitude of reverse induced electromotive force due to the complex augmented rails structure of the launcher. Meanwhile, the firing sequence of the pulse forming network disturb the detected muzzle voltage signal as system noise interference. Therefore, it is difficult to accurately calculate the contact resistance. To solve this problem, a noise suppression method of muzzle voltage system based on VMD-OptShrink is creatively utilized to suppress jagged noise. In this method, variational mode decomposition (VMD) can decompose the muzzle voltage signal in time-frequency domain according to the frequency characteristics. Then OptShrink is used to extract the low-rank components of the decomposed signal to obtain the denoised muzzle voltage. Finally, the contact resistance is calculated to analyze the armature-rail contact characteristics. The test results show that this method can suppress the muzzle voltage system noise well. The calculated armature-rail contact resistance waveform is smooth, which is conducive to the analysis of the armature-rail contact characteristics. The armature-rail contact resistance decreases rapidly at the initial stage of launching, then it fluctuates slowly until the armature slides out of the muzzle and the contact resistance increases sharply. The method proposed in this paper provides a new and reliable reference for the launching performance monitoring of electromagnetic railgun.