An event interative predictor for water rocket flight was developed using MATLAB. This proposed predictor can be used to solve the problem of phase II as well as strutz performed on sepreadsheet. it uses variation of specific mass as the consequence of the compression. using the initial temperature are 20 deg C and 25 deg C in shootinger model it needs 0 06 sec to finish the phase II which enhances accuracy of the prediction is 20%. it also shows that the temperature decrease when the fluid in Water Rocket expanding.