The invention is applicable to the technical field of distribution network planning, and discloses a method and system for determining the maximum photovoltaic access quantity, and a terminal device.The method comprises the following steps: obtaining a first data file of a preset power network and access data of a distributed photovoltaic network; adding the access data to the first data file toobtain a second data file, and calculating the first power flow of the second data file based on the constraint condition that the voltage of each node does not exceed the voltage range correspondingto each node to obtain the first maximum access quantity of the distributed photovoltaic; converting the first data file into a third data file; acquiring the planned access quantity of distributed photovoltaic, and generating an initial population according to the planned access quantity; according to the third data file, obtaining a second maximum access quantity of the distributed photovoltaicaccording to the initial population and the constraint conditions; and determining a target maximum access amount of that distribute photovoltaic accord to the first maximum access amount and the second maximum access amount. The invention can improve the accuracy of calculating the maximum photovoltaic access quantity.