The invention discloses an automobile fuel tank fuel quantity estimation method and system. The method comprises the steps that firstly, the system detects the pitch angle and the roll angle of the current whole automobile and conducts timing or timing zero clearing; 2, reading a measured value Vi of a sucker rod sensor, continuously measuring for N times, and solving a mean value or a smooth filtering value of V1-VN to obtain a current liquid level L; 3, implementing a Kalman filter; fourthly, the optimal value, estimated in the third step, of the current oil mass is sent to an oil mass display module; 5, the process is executed circularly, and the fuel quantity of the fuel tank is updated continuously. The invention further provides a system for estimating the fuel quantity of the automobile fuel tank. According to the method, an oil tank and an oil rod sensor are calibrated to obtain a liquid level-oil quantity curve, then the oil quantity value is continuously iterated and updated through the method, and the estimation precision problem is solved through steady-state continuous correction and unsteady-state continuous data fusion.