The invention discloses a method for optimizing a PI parameter of a high-voltage direct-current transmission constant-current controller. The method includes the following steps of firstly, using a high-voltage direct-current transmission quasi-steady-state model as a calculation model for parameter optimization; secondly, calculating a target function; thirdly, initiating an algorithm parameter; fourthly, calculating the feasible region of the PI parameter; fifthly, optimizing a genetic algorithm; sixthly, embedding a simplex method to judge the condition; seventhly, optimizing a mixed algorithm. The method relies mainly on the genetic algorithm while the simplex method subsidiary, the simplex method is embedded after optimization of the genetic algorithm tends to stop, and the advantages of local optimization of the simplex method are utilized while the individual variation and the global optimization capacity of population of a traditional genetic algorithm are kept. The simplified mode, namely, the quasi-steady-state model which is widely adopted during direct-current power transmission engineering calculation, is adopted, and therefore the calculation speed is high, the calculation accuracy meets the engineering requirements, the method is suitable for optimizing the parameter of the direct-current transmission system controller, and the degree of combination between the method and practical engineering is high.