A low speed synchronization method for a synchro-self-shifting clutch having a low speed protection function, characterized in that there is a critical rotational speed interval from an invalid state to activation state of the pawl for the synchro-self-shifting clutch having a low speed protection function and the method comprises steps as: determining that a critical speed interval of the synchro-self-shifting clutch is n1-n2 r/min, and setting a synchronization target rotational speed of an input end and an output as M r/min, where M>n2; increasing a rotational speed of the output end to M r/min and keeping the rotational speed at M r/min, and then increasing a rotational speed of the input end, the synchro-self-shifting clutch to be automatic meshed when the input end has a trend to make its rotational speed more than the rotation speed of the output end; wherein the term low speed in low speed synchronization method indicates a speed under a lower rotational speed to be less than a rated working rotational speed, and closed to the critical rotational speed interval n1-n2 r/min; in a case that the rotational speed of the input end is increased to n r/min, and tripping occurs at the output end when n1<n<n2, speeding up the increase of the rotational speed of the input end, and controlling the time needed for increasing the rotational speed of the input end from n r/min to n2 r/min to be less than the time needed for reducing the rotational speed of the output end from M r/min to n2 r/min, so that the rotational speed of the input end and the rotational speed of the output end are coincided with each other when the rotational speeds thereof are greater than n2 r/min, in order to achieve the synchro-self-shifting clutch to be automatically meshed, to avoid the rotation speed of the input end and the rotational speed of the output end to be coincided with each other within a critical rotational speed interval of n1-n2 r/min when tripping occurs; wherein, n1 indicates the upper limit of the critical rotational speed interval, n2 indicates the lower limit of the critical rotational speed interval, M indicates synchronization target rotational speed which is less than a rated working rotational speed, and closed to the critical rotational speed interval n1-n2 r/min, and n indicates a rotational speed greater than the lower limit n1 and less than the upper limit n2 in the process of increasing the rotational speed of the input end. in a case that the rotational speed of the input end is increased to n r/min, and tripping occurs at the output end when n1<n<n2, speeding up the increase of the rotational speed of the input end, and controlling the time needed for increasing the rotational speed of the input end from n r/min to n2 r/min to be less than the time needed for reducing the rotational speed of the output end from M r/min to n2 r/min, so that the rotational speed of the input end and the rotational speed of the output end are coincided with each other when the rotational speeds thereof are greater than n2 r/min, in order to achieve the synchro-self-shifting clutch to be automatically meshed, to avoid the rotation speed of the input end and the rotational speed of the output end to be coincided with each other within a critical rotational speed interval of n1-n2 r/min when tripping occurs; wherein, n1 indicates the upper limit of the critical rotational speed interval, n2 indicates the lower limit of the critical rotational speed interval, M indicates synchronization target rotational speed which is less than a rated working rotational speed, and closed to the critical rotational speed interval n1-n2 r/min, and n indicates a rotational speed greater than the lower limit n1 and less than the upper limit n2 in the process of increasing the rotational speed of the input end. <EOS>