Synthesis method of L-carnitine

The invention discloses a synthesis method of L-carnitine with a structure shown in a formula (1), which adopts L-(-)-3-cyan-2-hydroxyl propyl trimethylamine halide as a raw material and is prepared by hydrolysis and ion exchange; the hydrolysis is carried out in the following steps: in alkaline solution, hydrogen peroxide is used for hydrolyzing the L-(-)-3-cyan-2-hydroxyl propyl trimethylamine halide, and after full reaction, the hydrolysis reaction liquid is obtained. In the technique disclosed in the invention, the reaction condition is mild, the reaction time is short, the reaction yield is high, three wastes are less, and the implementation value and social and economic benefits are larger.