The invention discloses a method for low-temperature refining, bleaching and surface cleaning treatment of a cotton knitted fabric by virtue of a one-bath process. The method comprises the following steps: adding 3-10g/L of a biological enzyme for refining, 0.5-2g/L of cellulase, 3-10g/L of hydrogen peroxide, 2-6g/L of a bleaching activating agent, 2-8g/L of a chelating agent and 1-4g/L of an auxiliary agent into a one-bath system, regulating the pH value to be 6-7.5 by using an acid-alkali regulator, putting a fabric into a dye bath in a bath ratio of 1:(10-100), heating to 40-70 DEG C at a temperature rise speed of 0.5-2DEG C/min, preserving heat for 30-100min, and finally performing water washing, drying or airing on the fabric. According to the method disclosed by the invention, the bleaching activating agent and the biological enzyme are added into a one-bath low-temperature emigration system of the cotton knitted fabric to ensure that the refining, bleaching and surface finish treatment of the cotton knitted fabric are subjected to one-bath implementation under low-temperature conditions, the strength damage of the fabric can be avoided, the technological process can be shortened, the alkali amount and energy consumption can be reduced, and the processing efficiency of dyeing and finishing can be improved.