In order to obtain a better understanding of the non-ideal detonation behaviour of ammonium nitrate and fuel oil mixture explosive (ANFO), shock front curvature of stable detonation of ANFO was determined in steel and PMMA tubes. ANFO was initiated by a plane shock wave from a plane wave lens made by two kinds of liquid explosive, and the shock front trace was recorded with the streak camera. Based on the experimental results the radius of the shock front curvature of detonating ANFO with the detonation velocity of 1.7 km/s in a PMMA tube with the diameter of 40 mm was determined as 36 mm. While the radius of the shock front curvature in a steel tube with the diameter of 36 mm was determined as 55 mm with the detonation velocity of 3.1 km/s. The reaction zone length of detonating ANFO was estimated as 6.3 mm in a PMMA tube and 5.4 mm in a steel tube with Wood-Kirkwood equation. It was found that the confinement of ANFO had a strong influence on the detonation velocity and the detonation front curvature.