The trembling bow, also known as the shaking bow or the broken bow, is one of the common bowing methods of the erhu, and its symbol is "///", which is written at the bottom right of the note. The trembling bow is to use the bow to push and pull quickly and repeatedly, so as to produce a sound like the pipa's round fingers, and its actual effect is the homophonic repetition of the thirty-second note. This kind of bowing is more convenient to play crescendo, crescendo or free extension. It is often used to describe the vast, quiet and distant artistic conception when playing weakly. When playing strong, it is mostly used to express excited emotions and render a warm atmosphere.

The tremolo bow is very similar to the fast bow in its playing method. It also places the "axis" of the action in the middle of the forearm, so that the elbow and wrist become the two ends of the balance. The slight nervous vibration of the forearm drives the elbow to vibrate, and through the action of the "axis", the wrist and fingers naturally drive the bow to move in parallel to the left and right quickly.

The difference between the trembling bow and the fast bow is:

1. The frequency of changing bows of trembling bows is much faster than that of fast bows;

2. The number of notes in the fast bow is controllable, while the number of notes in the trembling bow is uncontrollable, and it can be vibrated eight or ten times per beat;

3. The bow part of the trembling bow is often changed according to the strength of the force, while the bow part of the fast bow is generally placed in the middle of the bow;

4. The fast bow requires clear pronunciation, and each sound should be in the shape of dots, so the string should be firmly attached; the trembling bow requires fine tremors, so that the pronunciation is composed of points and lines, so the string sticking degree is smaller than that of the fast bow.

It is very important to play the tremolo bow well, that is, the upper arm should be slightly tense to support the forearm. But we must pay attention to control the proper tension of the big arm. Too much tension will make the pronunciation stiff and not durable; if it is too loose, it will be difficult to control the bow and the pronunciation will be blurred. The parts below the forearm should be relatively relaxed, so that the upper part (referring to the upper arm) and the lower part (referring to the forearm, wrist and fingers) should be tightened. When a trembling bow is played weakly, the bow part can be close to the bow tip, the string should not be attached too tightly, and the amplitude of the tremor should be small, usually about one or two centimeters, but the frequency must be fast. When playing strongly, the bow can be used close to the middle bow. The string should be firmly attached, and the vibration amplitude should be large, generally more than five centimeters, and the frequency is not necessarily too fast. Whether the bow is strong or weak, attention should be paid to the uniformity of the tremor and to avoid the unbalanced tendency of pulling and pushing the bow.

There are three main problems that erhu learners are prone to in bowing:

First, the tension control or distribution of the arm is not appropriate;

Second, the frequency is too slow or the tremor is uneven, so that the effect of the trembling bow becomes "a mess of loose sand";

Third, the bow is not running straight enough, and moves in an oblique line or in a circle.