Embodiments of the present disclosure provide a method, controller, and system for controlling a dose in radiotherapy of a patient and a computer storage medium. The method includes: starting to time radiation of rays or calculate radiation dose of the rays before a source carrier is aligned with a collimator in a process of aligning of the source carrier and the collimator; irradiating rays to a target area of the patient through the collimator till the radiation dose of the rays received by the patient is equal to a radiation dose required for the radiotherapy. Therefore, the radiation dose of the rays received by the patient in an entire treatment process may reach the radiation dose actually required during the radiotherapy, thereby improving a radiation dose control accuracy and a treatment effect during the radiotherapy.