The invention provides a method and a device for estimating dose distribution change, and a method and a system for direct machine parameter optimizing. The estimation method comprises the following steps of determining the initial dose distribution before a blade is moved; in the initial dose distribution, determining the dose change influence range caused by the blade moving; for an interest point in the dose change influence range, according to the initial dose distribution, obtaining the initial dose of the interest point before the blade moving, determining a reference point correlated with the interest point because of the blade moving, and according to the dose of the reference point in the initial dose distribution, obtaining the current dose of the interest point after the blade moving; according to the initial dose and the current dose of the interest point, calculating the dose change of the interest point. The estimation method has the advantages that the estimation accuracy on the dose distribution change is higher, the calculation speed is high, the calculation amount is less, the memory occupation is less, and the like.