We report an equivalent circuit model for MEMS (microelectromechanical systems) electrostatic actuator using open-source circuit simulator Qucs (quite universal circuit simulator). Electrostatic force, equation of motion, and Kirchhoff's laws are implemented by using the EDD (equation defined device) function of Qucs. Mathematic integral operation in the equation of motion is interpreted into electrical circuits by using an ideal electrical capacitor that read input signal as current and returns accumulation result in terms of voltage. Seamless multi-physics mixed signal simulation between micro mechanics and electronics has become possible on the single platform of the circuit simulator.