The invention relates to a quantitative analysis method of solution chromogenic reaction and a detector thereof. According to the invention, by utilizing the photopermeability characteristics of a solution generated by reaction between chromogenic substances and a chromogenic agent, and utilizing a calculation module designed according to color space concept, the three primary colors including red, green and blue which are shown by transmission light are converted into measurement points shown by performance numbers including lightness, green-red and blue-yellow, the hue and target color difference of the solution are calculated, a standard curve of hue, target color difference and concentration of chromogenic substances is fitted by a polynomial expression, and the concentration of a practical sample is calculated by an interpolation method. According to the principle, the designed detector consists of an upper computer and a lower computer which are connected by a communication data line (16), and comprises a lower computer circuit (5), a sample cell (2), an LED light source (14), an upper computer circuit (18), a color collecting system, a data acquisition and processing system, an operation system and working procedures. The detector is simple in structure, is convenient and rapid to operate, is accurate in result, and can be widely applied to the quantitative detection of the solution chromogenic reaction.