The invention relates to an adjustable waist protector comprising two binding belts, two support assemblies, a first tightness adjusting assembly and a second tightness adjusting assembly. Each binding belt comprises a first terminal and a second terminal, and the first terminals of the two binding belts are opposite to each other and are spaced from left to right. The two support assemblies are respectively arranged on the two binding belts and are close to the first terminals, each support assembly comprises an upper terminal, a lower terminal and a plurality of guiding parts, and the number of the guiding parts is an odd integer. The first tightness adjusting assembly comprises a first stay cord, and the first stay cord penetrates through one support assembly and is wound on parts, of the guiding parts of the two support assemblies, being close to the upper terminals. The second tightness adjusting assembly comprises a second stay cord, and the second stay cord penetrates through the other support assembly and is wound on parts, of the guiding parts of the two support assemblies, being close to the lower terminals. Thus, the tightness degree of the upper half parts and the tightness degree of the lower half parts of the two binding belts can be adjusted respectively, and the two binding belts are actually affixed to the waist curve during the binding process.