The invention discloses a boom telescoping control method, a boom telescoping control apparatus, a boom telescoping control system and an engineering machine. The method comprises the following steps: acquiring the target telescoping length of a boom; acquiring the current telescoping length of the boom in real time; determining a telescoping control signal according to the current telescoping length of the boom and the target telescoping length of the boom; and outputting the telescoping control signal to an execution mechanism in order to control the boom to telescope. The current telescoping length of the arm is acquired to realize real time adjustment of the telescoping control signal, so improvement of the stability in the boom telescoping process is facilitated, and the pressure impact of a hydraulic system is reduced; and closed loop control is adopted to realize the consistence of the boom telescoping rules under different conditions, so the telescoping efficiency is guaranteed.