We have done a survey about the surface crack of the loess tunnel of Zheng-xi passenger railway by field survey, geophysical exploration test and pit detection and also have researched the produced regularity of the surface crack of the loess tunnel, especially about in the depth. The result of the survey and the detection indicates that: (1)The surface crack is mostly visible in the shallow area of the loess tunnel entrance. The visible width of the surface is extensive (0.2~200mm) and it is mostly visible in the tunnel, the depth of which is below 60m. The visible or wide cracks mostly appear in the area whose surface settlement is above 80mm. The width of the surface crack of the tunnel, which has a more shallow depth and a larger settlement, is much wider. (2)The effect of the High-density electrical method reflecting the development of the surface crack is obvious. The method of seismic reflection wave and seismic imaging is more accurate than Rayleigh wave in interpreting depth development of the crack. (3)There are two kinds of performance of the surface crack: longitudinal crack that inclines to the inside on both side of the tunnel and circumferential crack perpendicular to the axis of the tunnel. (4)The visible crack depth of the surface crack is limited, which is about 3.0~10m and it always doesn't reach the top of the tunnel. The depth by the geophysical exploration test is much more depth, which is about 10~15m.