The invention discloses a positive thermo-sensitive lithographic printing plate precursor. A resin layer and a thermo-sensitive layer are sequentially coated on the upper side of a supporting body of a hydrophilic surface; the resin layer comprises alkali-soluble resin; and the thermo-sensitive layer comprises the alkali-soluble resin and an infrared absorption agent. The precursor is characterized in that: the resin layer comprises the alkali-soluble resin and the infrared absorption agent; the alkali-soluble resin comprises -L1-L2-R acrylic resin with a side chain structure; one of the L1 and the L2 is -HN-, and the other of the L1 and the L2 is -CH2-; and the R is any one of H, an alkyl group, a phenyl group or a substitute phenyl group. The positive thermo-sensitive lithographic printing plate precursor of which the resin layer comprises the alkali-soluble resin and the infrared absorption agent has high solvent resistance, high sensitivity and high development tolerance level.