Disclosed are an apparatus and a method for measuring the height of a solid bed in a high-temperature and high-pressure fluidized bed system, and a fluidized bed system having the solid bed height measuring apparatus. The solid bed height measuring apparatus includes a lower pressure probe mounted at an upper side as high as a first height from a gas distributor of a fluidized bed reactor to measure pressure of the mounted location, and a middle pressure probe mounted at an upper side as high as a second height from the lower probe to measure pressure of the mounted location. An upper pressure probe is mounted at the top of the fluidized bed reactor to measure the inside pressure of the fluidized bed reactor. First and second differential pressure gauges are used for measuring differential pressures.