The invention relates to a lamp frequency control system for a display and method for controlling the lamp frequency. The lamp frequency control system comprises a driving control device and a lamp frequency control device. The driving control device has a driving mode selector for selecting a driving mode from at least two driving modes. According to the selected driving mode, the driving mode selector outputs at least one corresponding frequency control signal. According to the corresponding frequency control signal, the lamp frequency control device obtains at least one corresponding lamp frequency. According to the various driving mode, the lamp frequency control system of the invention obtains the corresponding lamp frequency. That is, the lamp frequency can be adjusted to match the driving mode. Therefore, the lamp frequency can be adjusted at a frequency section without the water flow interference. The lamp frequency control system of the invention can resolve the water flow interference.