The invention relates to a forecasting and correcting method for joining a main deceleration stage and an approaching stage. The forecasting and correcting method includes the steps of calculating main deceleration stage guidance parameters, conducting rapid adjustment stage terminal forecasting based on the main deceleration stage guidance parameters and current states of a detector, correcting a main deceleration stage guidance target based on approaching stage inlet conditions, judging whether main deceleration switching conditions are met or not, switching into rapid adjustment guidance if the approaching stage switching conditions are met, otherwise, executing the first step, the second step and the third step again until the main deceleration switching conditions are met, determining rapid adjustment stage guidance parameters according to switching time states, determining current guidance commands according to the rapid adjustment stage guidance parameters, planning approaching stage inlet guidance commands according to the current state, and when an included angle of rapid adjustment stage current guidance commands and the approaching stage inlet guidance commands is smaller than a set value, or the guidance time is completed, switching into approaching stage guidance. According to the forecasting and correcting method, requirements of an approaching stage inlet for gestures, heights, speeds and accelerated speeds are met, and the requirement of the detector for transiting from the main deceleration stage to the approaching stage is met.