在利用气垫导轨装置及配件进行的各类实验中，速度作为一个基本的待测量，其准确测量有着重要的意义.通常利用MUJ-6B 通用计数器记录不同类型挡光片经过光电门的遮光时间，用游标卡尺测得遮光距离从而得到速度值.本文从光电计时原理分析了使用U 形挡光片、计时方式2 不会出现系统误差，而使用条形挡光片、计时方式1 会出现较大系统误差的原因.我们进一步利用气垫导轨上两弹簧连接滑块做简谐振动模型的理论公式推导出条形挡光片遮光时被光电门“吞掉”的宽度，进而得到了速度的修正公式.此外，通过气垫导轨上的动量守恒实验从另外一个角度验证了速度修正方法的正确性.

In all kinds of experiments using air track with accessories and spare parts，whether direct or indirect measurement，velocity is a basic physical quantity to be determined and the accurate measurement of velocity is of great significance. Universal counter MUJ-6B is often used to record the blackout time as different type of light barrier passes through the optical gate，while the vernier caliper is used to measure the blackout distance，then the value of velocity is obtained. From the viewpoint of the principle of photoelectric timing，this article analyzes the reason that there is no systematic error with U-shape light barrier using timing mode 2，while there is great systematic error with strip light barrier using timing mode 1. Moreover，the“swallowed”width of strip light barrier by photoelectric gate is deduced by using the theoretical formula of harmonic vibration model which is realized by two springs and a slider moving on the air track. Hence，the modified formula of velocity is obtained，which is tested and verified by the experiment of momentum conservation on the air track. Therefore，the proposed velocity correction method is tested to be reliable from another aspect.