The invention discloses a block polyether compound modified 
lignin and a preparation method, which includes the following steps: a pressure-resistant reactor is firstly carried out the 
vacuum pumping, the 
nitrogen is added to the normal pressure, the 
oxygen is removed, after that, 100 weight parts of the purified 
lignin, 0.1 to 5 weight parts of base catalyst, and 20 to 100 weight parts of aromatics 
solvent are taken; the 
nitrogen is introduced for protection after the feeding, the pressure-resistant reactor is confined and stirred, 10 to 100 weight parts of 
ethylene oxide and 
propylene oxide are divided into 2 to 10 equal parts at 80 to 150 DEG C and 0.3 to 1.0 MPa, one equal part of 
ethylene oxide is introduced during each time of reaction for reaction for 30 to 60 minutes, one equal part of 
propylene oxide is then introduced for reaction for 30 to 60 minutes, after that, one equal part of 
ethylene oxide is introduced for reaction, the reaction is stopped after 2 to 10 times of such cyclic reactions, the heating is also stopped, and the mixture is cooled down to the 
room temperature, then the stirring is stopped, the 
nitrogen is introduced to enable the pressure-resistant reactor to achieve the normal temperature, finally the product is obtained by removing the 
distillation fractions with the low boiling points by 
vacuum distillation. The product can be used as a surfactant and can also be applied to the manufacture of rigid 
polyurethane foam materials.