The invention relates to a determination method based on an ANSYS second development platform of the initial completion initial cable force of a cable-stayed bridge. The method uses the design cable force as the target value, considers the geometric non-linear effect and performs iteration for solving and correcting the cable initial strain under the action of dead load. The method comprises the following specific steps: any group of cable forces is assumed to be added on the stay cable in the mode of initial strain, dead load is added to calculate, the *do-loop command language is used to extract the calculated cable force of the stay cable and check whether the error between the cable force and the target completion cable force is within an available limit; if the error is large, the indifference method is used to correct the stay cable initial strain, then the error is calculated again until the error is within the available limit; and the initial completion initial cable force canbe obtained by multiplying the last calculated group of stay cable initial strains by the elastic modulus of the stay cable which is corrected by considering the vertical effect. By using the method,the solving time of the completion initial cable force of the cable-stayed bridge can be reduced and the precision can be increased, thus the method has large practical engineering application value.