Objective To explore the influence of ambroxol hydrochloride combined with fiberoptic bronchoscopy alveolar lavage （BAL） on the clinical symptoms， the absorption of lung consolidation， and the levels of mucin 5AC （MUC5AC）， phosphatidylinositol 3-kinase （PI3K）， and soluble programmatic death factor ligand-2 （sPD-L2） in children with mycoplasma pneumoniae pneumonia （MPP） accompanied by mucus thrombus in the airway. Methods A total of 102 children diagnosed with MPP accompanied by airway mucus thrombus， who were admitted to the hospital from June 2024 to October 2025， were randomly assigned to the study group （n = 51， receiving conventional comprehensive treatment plus bronchoscopy BAL with ambroxol hydrochloride mixed in normal saline） and the control group （n = 51， receiving conventional comprehensive treatment plus bronchoscopy BAL with simple normal saline） using the random number table method. The disappearance time of high fever， cough， pulmonary rales， and mucus plugs， the length of hospital stay， and the absorption of pulmonary consolidation were compared between the two groups. Respiratory mechanics， including lung volume （LV）， lung static compliance （Cstat）， and airway plateau pressure （Pplat）， as well as the levels of serum C-reactive protein （CRP）， white blood cell count （WBC）， interleukin-6 （IL-6）， and interferon-γ （IFN-γ） were detected and compared between the two groups before treatment and 10 days after treatment （post-treatment）. Bronchoalveolar lavage fluid （BALF） was collected during the first bronchoscopy BAL and on the 3rd day after the last BAL treatment， and the levels of MUC5AC， PI3K， and sPD-L2 in the BALF of the two groups were measured and compared. Meanwhile， the adverse reaction rates during the treatment period in both groups were statistically analyzed. Results The disappearance times of high fever， cough， pulmonary rales， and mucus plugs， as well as the length of hospital stay， were all shorter in the study group than those in the control group （P < 0.05）. Moreover， the classification of lung consolidation absorption area was more favorable （P < 0.05）. In comparison with the pre-treatment status， both LV and Cstat increased in both groups after treatment （P < 0.05）， whereas the levels of Pplat， serum CRP， WBC， IL-6， and IFN - γ decreased （P < 0.05）. When compared with the results of the first bronchoscopy BAL， the levels of MUC5AC， PI3K， and sPD-L2 in the BALF of both groups decreased on the 3rd day after the last BAL treatment （P < 0.05）. Additionally， the extent of decrease or increase of the above-mentioned indicators was greater in the study group than that in the control group （P < 0.05）. There was no statistically significant difference in the adverse reaction rates between the two groups （15.69% vs. 21.57%） （P > 0.05）. Conclusions Ambroxol hydrochloride combined with bronchoscopy BAL can effectively promote the relief of clinical symptoms and signs and the absorption of lung consolidation in children with MPP accompanied by mucus thrombus in the airway， and improve their respiratory mechanics. The mechanism of action may be related to the down - regulation of MUC5AC， PI3K， and sPD-L2 levels in BALF.