Abstract: Equations describing the potentiometric stripping analysis (PSA) with a hanging mercury dropping electrode (HMDE) are deduced. Transition time equation and E-t curve equation are obtained and quantitative relationship between transition time and parameters, e.g., the cocentrations of determined ions and oxidant preconcentration time, electrode radium, etc, is also obtained. All the theoretic conclusions were verified experimentally, and the results are in agreement with the theory.