This paper briefly introduces the measuring principle and structure of the liquid level standard device, which is based on the double-frequency laser interferometer equipment for measuring the liquid level. An uncertainty evaluation mathematical model for the liquid level standard device has been established. In the studies, various uncertainty affecting the liquid level standard device were analyzed. Based on this, the uncertainty components of different influence factors were calculated. The results show that the uncertainty value of the liquid level standard device was 0.045 588 mm, and the expanded uncertainty was 0.091 176 mm.