Objective To compare the bacterial spectrums of respiratory intensive care unit (RICU) patients derived from traditional bacterial culture and loop-mediated isothermal amplification (LAMP) assay. To analyze the relationship between clinical factors and clinical outcome of patients. Methods Data of patients in RICU with lower respiratory tract infection from October 2018 to December 2020 was collected. The bacterial spectrums obtained by traditional culture method and LAMP-based method were compared. Clinical factors were divided into two categories and taken into analysis of variance for assessing their relevance with clinical outcomes. Those with significances in analysis of variance were taken into binary logistic regression. Results A total of 117 patients were included. The ratio of patients with positive bacterial culture results was 39.13% (n=115), and that with positive LAMP assay results was 72.65% (n=117). The ratios of patients with at least two positive results for culture and LAMP were 8.70% (n=115) and 36.75% (n=117), respectively. According to chi-squared test, mechanical ventilation (χ2=5.260, P=0.022), and patients with two or more bacteria positive for LAMP assay (χ2=8.227, P=0.004) were related to higher risk of death. Mechanical ventilation and patients with two bacteria positive for LAMP assay were included in binary logistic regression. The odds ratio for death was 4.789 in patients with two or more bacteria positive by LAMP assay (95% confidence interval 1.198 - 19.144, P=0.027). Conclusions LAMP-based method is helpful in detecting more bacteria from respiratory tract specimens of RICU patients, which will be a contributor to precision medicine. Patients with at least two bacteria positive based on LAMP assay have higher risk of death.