The invention discloses a lane deviation control assisting method based on steering and braking extendable joint. The lane deviation control assisting method comprises the steps of after a lane deviation assisting system is started, extracting a pavement attachment coefficient Mu and an initial steering wheel corner theta0 as characteristic variables to constitute a character state S (Mu, theta0)and building an extendable set space related to the character state S (Mu, theta0); dividing the extendable set space, and according to the divided extendable set space, calculating a correlation function related to extendable joint control in different set states; according to a range field of the correlation function, dividing a control field into a non-field, an extendable field and a classicalfield. An electric steering control method is adopted in the non-field, a differential braking control method is adopted in the classical field, and a steering and braking joint control method is adopted in the extendable field; the lane deviation assisting system judges a control field according to the real-time state of the vehicle, and torque and a braking signal which are obtained in the control field according to the corresponding control method are input to a vehicular access model.