The invention discloses an amplification circuit in a servo motor. The amplification circuit comprises a primary amplification circuit, a secondary amplification circuit and a third-stage amplification circuit, wherein the primary amplification circuit is connected with an input circuit; resistors, capacitors, diodes and transistors are sequentially combined to be a whole to form the primary, secondary and third-stage amplification circuits; a signal enters the secondary amplification circuit after being amplified by a differential circuit in the primary amplification circuit, and a booster circuit is arranged in the secondary amplification circuit, so that it ensures that intensity of the signal of an input end continues to be stable in the secondary amplification circuit after being amplified by the primary amplification circuit without causing signal attenuation, then the signal is output to production equipment via the third-stage amplification circuit, and thus stable and step-by-step amplification and transmission of the signal are achieved, the production equipment is continuously and stably driven to work, and work efficiency is improved.