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This study focused on hydraulic characteristics around a gear-shaped weir in a straight channel. Systematic experiments were carried out for weirs with two different gear heights and eight groups of geometrical parameters. The impacts of various geometrical parameters of gear-shaped weirs on the discharge capacity were investigated. The following conclusions are drawn from the experimental study: (1) The discharge coefficient (mc) was influenced by the size of the gear: at a constant discharge, the weir with larger values of a/b (a is the width of the gear, and b is the width between the two neighboring gears) and a/c (c is the height of the gear) had a smaller value of mc. The discharge capacity of the gear-shaped weir was influenced by the water depth in the weir. (2) For type C1 with a gear height of 0.01 m, when the discharge was less than 60 m3/h and H1/P < 1.0 (H1 is the water depth at the low weir crest, and P is the weir height), mc significantly increased with the discharge and H1/P; with further increases of the discharge and H1/P, mc showed insignificant decreases and fluctuated within small ranges. For type C2 with a gear height of 0.02 m, when the discharge was less than 60 m3/h and H1/P < 1.0, mc significantly increased with the discharge and H1/P; when the discharge was larger than 60 m3/h and H1/P > 1.0, mc slowly decreased with the increases of the discharge and H1/P for a/b ≤ 1.0 and a/c ≤ 1.0, and slowly increased with the discharge and H1/P for a/b > 1.0 and a/c > 1.0. (3) A formula of mc for gear-shaped weirs was established based on the principle of weir flow, with consideration of the water depth in the weir, the weir height and width, and the height of the gear.