In accordance with Landau's theory on phase transition, a theoretical analysis has been made for the nonequilibrium phase transition in the operation of a fibre-coupled semiconductor OBI) with feedback pumping. It is shown that the feedback paiameter is the transitional condition from the second-order phase transition to the first-order phase transition. Parameters of three operation modes and signal amplification and processing have been reduced. respectively. The theory agrees with the author's experimental results.