The invention discloses a regulating method for a speed regulator mechanical open limit of a generation set. The method comprises the following steps of setting the speed regulator mechanical open limit value corresponding to a connected-grid initial load value after the generation set is connected to a grid, and enabling the speed regulator mechanical open limit value to be maintained in a scope of 63 percent of a mechanical open limit full open value; and when the generation of the set reaches a stable state, corresponding regulation is carried out on the speed regulator mechanical open limit through a monitoring system according to different up and down reservoir water level differences. According to the technical scheme, the speed regulator mechanical open limit is intelligently controlled by the monitoring system according to the change of an operating head, on the premise of a full load, the opening degree of guide blades is enabled to be in a controlled margin scope of the speed regulator mechanical open limit all the time when under regulation of different heads, so that the reduction on risk of an overload is realized, and the reliability of device operation is improved.