Abstract: A Venetian blind is provided with a slat-lifting mechanism consisting of a slat set, a slat pull cord, and a constant torque pull set. The slat set has a plurality of slats. The slat pull cord is connected with each of the slats of the slat set and is put through the bottommost end of the slat set. The constant torque pull set is disposed at the top end of the slat set and composed of a pull cord member and a constant torque spring unit which is linked with the pull cord member and provided with a constant torque spring which has a constant retrieving force enabling the pull cord member to rewind. The constant retrieving force of the constant torque spring must meet the condition of W-Fs<R<W+Fs, in which W stands for a total weight of the slat set; Fs, a system static friction force; and R, a retrievable elastic force of the constant torque spring.