The invention relates to a cellulose in-situ urea modified plastification melt spinning method comprising the following steps of: (1) drying the cellulose and the urea under a vacuum condition; (2) uniformly mixing 10-20wt% of cellulose, 50-70wt% of ionic liquid and 10-40wt% of urea; (3) extruding the mixture by a co-rotating twin screw extruder, defoaming, filtering and ejecting from a spinneret port; (4) drawing and coiling the quickly solidified fiber to form cellulose fiber. The method can be used for get the cellulose grafted copolymer which is easy to process, high-efficiency, green and clean, and can prompt development of the novel cellulose fiber which is low in energy consumption, economical, practical and environmentally-friendly.