The invention discloses a continuous casting tundish liquid level stability controlling method and system. The continuous casting tundish liquid level stability controlling method comprises the following steps of collecting and preprocessing liquid level weight signals; according to the collected liquid level weight signals, calculating a liquid level weight change rate by adopting a least squarecurve fitting algorithm; and according to liquid level weight deviation and the liquid level weight change rate, adopting a fuzzy control algorithm and calculating output time of an one-time hydraulicvalve through a control rule base. According to the continuous casting tundish liquid level stability controlling method, the control precision is high and can reach the level of less than or equal to 0.3 t, liquid level fluctuation is small, and the pulse width control with the optimal output can greatly reduce the liquid level adjusting frequency, so that the service life of the hydraulic valveis prolonged.