Abstract: The article brings forward the concept of microwelding in the field of resistance weld and discusses the requirement of welding power source for microwelding.The square pulse, whitch the adjustable minimum-setting scales are voltage amplitude of 0.01 V and pulse duration of 1 ms, is designed to step-pulse.The six adjustable parameters of the step-pulse include the pulse slip angle θ₁, the first and second step voltage amplitude and duration of the step-pulse(U₁, t₁, U₂, t₂), and the pulse declining angle θ₂.The function of the slip angle is to limit instant current impact, the first step-pulse is to strip or preheat, the second is to weld, and the declining angle is to postheat.Adapting to the requirement of stripping welding and microwelding for welding power, the step-pulse not only extends the life of welding tips for stripping weld, but also reduces spatter and improves welding quality.