The invention provides a horizontal well experimental system for a horizontal well section with an adjustable angle. The horizontal well experimental system comprises a gas source, an overhead oil tank, an overhead water tank, a metering device, an oil-gas-water mixing device, the horizontal well section with the adjustable angle, an oil-water separating tank, a ground oil tank and a ground water tank. The gas source, the overhead oil tank and the overhead water tank are respectively connected with the oil-gas-water mixing device and supply gas, oil and water respectively; the system is further internally provided with the metering device used for metering the gas, oil and water to generate metered data; the oil-gas-water mixing device is used for mixing the gas, the oil and the water and then inputting an obtained mixture to the horizontal well section with the adjustable angle; the horizontal well section with the adjustable angle is provided with an angle adjusting device; the oil-water separating tank is connected with the horizontal well section with the adjustable angle and used for separating oil and water and inputting the separated oil into the ground oil tank and the separated water into the ground water tank; the ground oil tank is connected with the overhead oil tank and supplies oil to the overhead oil tank; and the ground water tank is connected with the overhead water tank and supplies water to the overhead water tank.