The invention provides a construction method and system for improving secondary grouting quality used for shield construction. The method comprises following steps: firstly, determining a geological condition of a construction site; secondly, determining partitions of grouting slurries in order to carry out slurry performance; thirdly, determining grouting pressure P and grouting amount Q; fourthly, opening a grouting hole and connecting with a semi-automatic grouting platform car system; fifthly, preparing grouting slurries via the semi-automatic grouting platform car system to carry out secondary grouting; and sixthly, flushing a grouting pipe and a Y-shaped three-way pipe fitting. The construction method and system for improving secondary grouting quality used for shield construction has following beneficial effects: by depending on the semi-automatic grouting platform car system, the automatic stirring function of cement grout and water glass slurries and the semi-automatic adding function of grouting material are fulfilled; therefore labor and time of secondary grouting are effectively saved; precision of grouting slurry blending is increased; and uniformity and grouting efficiency of grouting slurries are enhanced.