The utility model discloses a telescopic fireproof coating thickness detection device. The device comprises a sliding sleeve, a sliding rod, a fixing assembly and a sliding pipe, the sliding rods arelocated on the inner sides of the sliding sleeves. A probe is arranged in the middle of the upper end of the sliding rod; a needle hole corresponding to the probe is formed in the middle of the upperend of the sliding sleeve; limiting sliding grooves are symmetrically formed in the left side and the right side of the sliding rod. Limiting sliding blocks corresponding to the limiting sliding grooves are symmetrically arranged in the middles of the left side wall and the right side wall in the sliding sleeve, a fixing assembly is arranged in the middle of the rear side of the sliding sleeve, scales are arranged on the lower portion of the front side of the sliding rod, a first telescopic rod is fixedly connected to the lower end of the sliding rod, and a first external thread structure is arranged on the outer side surface of the first telescopic rod. The device is simple to use, the length of the device can be manually adjusted, and a measurer can stand on the floor surface to directlymeasure the fireproof coating at the bottom of the steel beam, so that high-altitude operation is avoided, and the safety of the measurer is greatly improved.