The invention relates to a lung tissue single-channel fixing instrument and overcomes the defects that existing lung tissue fixing is low in speed, fixing liquid immersion efficiency is affected, the exposure time of lung tissues is excessively long, and the experiment result is affected. The lung tissue single-channel fixing instrument comprises a fixing body, the fixing body is internally provided with a containing cavity for containing fixing liquid, the fixing body is provided with an opening communicated with the containing cavity, a sealing cover is arranged at the opening, the side wall of the fixing body is provided with a side channel communicated with the containing cavity, and the side channel is internally provided with an air pulling core. As the air pulling core moves outwards, the volume of the containing cavity is increased, so that the pressure intensity in the containing cavity is lowered, a negative pressure state is formed, in the negative pressure environment, air in the lung tissues is discharged rapidly, under the elasticity of the lung tissues, the fixing liquid is immersed into pulmonary alveoli rapidly, and the pulmonary alveoli recovers to the original shape, so that lung tissue cells are integrally fixed, and subsequent immunohistochemistry and pathological analysis are facilitated.