The invention provides a no-iron treatment method for a cotton shirt, which can solve the problems of yellowing due to overhigh baking temperature and poor seam appearance due to seam shrinkage of the cotton shirt. The method comprises the following process flows: resin absorbing, pre-baking, pressing, baking and cooling, wherein a working solution comprises the following components in percentage by
mass: 15 to 25 percent of resin, 1 to 2.5 percent of catalyst and 2 to 4 percent of
fiber protective agent; and the pH value of the working solution is regulated to be between 4.5 to 5.0. The process can ensure that seams or pleats of collar, yoke, two sleeves, side seams, a left
front panel, a right
front panel, a left back panel, a right back panel and other parts of the shirt are flat and fitting, no bulge is generated after the shirt is washed, and all the appearance flatness of products and the appearance of the seams and the pleats are up to the 4.0 level of 'the No-iron Textiles Standard' published by the State Administration of Quality Supervision, Inspection and
Quarantine, namely the testing index is higher than 'the No-iron Textiles Standard' by 0.5 to 1 level.