本文根据多模激光时间相干性g（1）（τ）的准周期性特点，提出了一种观测多模激光纵横线型函数及其频宽的新方法──程差2kL法。文章介绍了测量原理与方法，并以双模He－Ne激光器为例，给出了相应的实验结果。研究表明，多模气体激光的纵横线型函数为洛仑兹外。（Lorentz）线型函数，相应的纵模频宽约为107Hz。 According to the quasiperiodic nature of the time coherence g (1) (τ) of multimode laser, a new method of observing the linear function and its bandwidth of multimode laser ─ ─ path difference 2kL method is proposed. The paper introduces the principle and method of measurement. Taking the dual-mode He-Ne laser as an example, the corresponding experimental results are given. Research shows that the multi-mode gas laser linear function Lorentz outside. (Lorentz) linear function, the corresponding longitudinal mode bandwidth is about 107Hz.