Abstract: Measurement of liquid level in sealed container from side wall is generally based on the difference of echo signal in solid-gas and solid-liquid interface. The technique of longitudinal wave vertical incidence was always used this method. However, it is unsuitable for the low impedance liquid because of small differences in the echoes amplitude. A new technique for measuring liquid-level utilizing angle wave is presented and demonstrated through simulation. Using this technique, the calculation and experiment of the composite interface of various containers and liquids are carried out. Results have shown that the optimum angle is related to the character of interface-material of container and the character of inner liquid. The difference of reflection coefficient at the best angle is higher than vertical incidence. The oblique incident wave is easier to detect and identify targets. The level measurement accuracy can reach a few tenths of centimeters while using the squared area method.