The invention belongs to the field of 
active carbon preparation, and particularly relates to modified composite 
biochar, a preparation method and applications thereof. The technical problem to be solved by the invention is to provide modified composite 
biochar, a preparation method and applications thereof. The preparation method comprises: A, carbonizing straws, washing off ash, 
drying, and crushing to obtain 
straw biochar; B, mixing the 
straw biochar, an alkali liquor, carrying out 
chemical modification, separation, washing the 
solid, and 
drying to obtain modified 
straw biochar; and C, carrying out compounding treatment: mixing the modified straw biochar, 
polyethylene glycol and water, adding MIEX, stirring, carrying out ultrasonic treatment, adding 
ascorbic acid or 
hydroxylamine, continuously stirring, adding a 
hydrogen peroxide solution, continuously stirring, separating, washing the 
solid, and 
drying to obtain the modified composite biochar. According to the method disclosed by the invention, the agricultural and 
forestry waste straw can be utilized to prepare the modified composite biochar with good adsorption performance.