The invention discloses a method for preparing an ultrasonic alkylated lignosulfonate bio-based surfactant, which belongs to the field of lignosulfonate alkylated synthesized surfactant. According to the method, the number of active groups of lignosulfonate is increased and the tidiness of the molecular structure is improved by using an environment-friendly and efficient ultrasonic wave activation technique, the defects that the industrial lignosulfonate is low in reaction activity and poor in tidiness of the molecular structure are overcome; the bio-based surfactant is synthesized from the lignosulfonate through alkylation in a mixture solution system of alkali organic solvents and water in the presence of pyridine and derivatives of pyridine serving as catalysts. The surface tension force of an aqueous solution of the bio-based surfactant with the mass concentration of 1% is as low as 28.2mN/m, and the critical micelle concentration is 5*10<-5>g/L. The surfactant has the advantages of low cost and characteristics of chemical environment-friendless, is possibly used for completely or partially replacing a petroleum base surfactant to be applied to daily chemical fields and is wide in application prospect.