The preparation process of water soluble ethoxyl chitin includes the following steps: 1. alkalifying reaction of chitin and alkali solution of 35-50 wt% at the temperature of -10 deg.c to 0 deg.c for 6-24 hr to produce alkalified chitin, and defreezing, squeezing and crushing the alkalified chitin into 10-100 mesh alkalified chitin powder; and 2. gas-solid reaction of alkalified chitin powder and gaseous ethylene oxide in some container at 20-50 deg.c through stirring for 1-6 hr, and purifying the reaction product to obtain the water soluble ethoxyl chitin. The process has high yield, complete reaction, less side reaction and no corrosion to the apparatus, and the prepared ethoxyl chitin has high water solubility.