Photoisomerization is a prototypical photophysical and photochemical reaction, and the reaction quantum yield depends on its excited-state dynamic. Changing the evolution path of molecular excited states to achieve precise control over photochemical reactions has long been a dream pursued by physicists and chemists. To investigate the effect of femtosecond laser pulse on the ultrafast reaction, the ultrafast photoisomerization of 1, 1'-diethyl-2, 2'-cyanine iodide (1122C) in methanol is studied using pump-dump-probe spectroscopy. A third femtosecond pulse (Dump) at 1030 nm, which is delayed by 1 ps relative to the initial pump pulse, is introduced into the traditional pump-probe experiment. The recovery of ground state bleaching (GSB) and decrease of the cis product are observed in the pump-dump-probe experiment. It indicates that the dump pulse successfully promotes the initial transform: skipping the trans-cis isomerization pathway in the excited state and returning to the ground state directly through stimulated emission. It is found that the cis yield is reduced by approximately 12.1% under irradiation of the dump pulse. Our research shows that the quantum yields of a typic ultrafast photoisomerization reaction is successfully regulated by using femtosecond laser pulse, demonstrating the potential of femtosecond multi-pulse spectroscopy in modifying excited-state evolution pathways and optimizing photochemical reaction yields. This study provides theoretical and technical support for precisely controlling complex photochemical reactions in the future.