The study of the primary mechanisms on effects of Ca and Mg applied in foliar nutrients on the pericarps coloring was conducted with Sanyuehong litchi fruits .The treatments included spraying the Ca，Mg solutions and their mixtures，and the check(CK)was sprayed with clean water.The results were the following:in the course of the development of the pericarps reddening，the different foliar nutrients treatments and CK all improved the contents of the corresponding elements in pericarp.The partial correlation coefficients between the content of total Ca and the watersoluble K，the total Mg and the total Ca，the watersoluble K and the total Mg，the watersoluble Mg and the total Ca were significant positive in all the treatments and CK.The multiple correlation coefficients between one of the contents of the total and the watersoluble K，Ca and Mg and the other five ones rest were respectively significant.The treatment Ca+Mg successfully solved the problem that the peel kept green at the total soluble sugar in flesh rising to the top，and the treatment Mg successfully solved the problem that the total soluble sugar in flesh dropped at the percarps full reddening.The higher content of the watersoluble Mg in pericarp of the treatment Mg and CK was the key factor for improving the pericarps reddening，the higher content of the total Ca in pericarp of the treatment Ca was the key factor for improving the pericarps reddening，and the higher content of Ca and watersoluble Mg in pericarp of the treatment Ca+Mg was the key factor for improving the pericarps reddening.To the different treatments and CK，the exponential regression equations of the contents of the anthocyanin to those of the total Mg，the watersoluble Ca and the total Ca in pericarp indicated significant respectively positive correlations，while the exponential regression equations of the contents of the chlorophyll to those of the watersoluble Ca in pericarp were significant respectively negative correlations.In conclusion，the element Ca and Mg had a synergistic effect on the growth and development of pericarp in Sanyuehong litchi，and different treatments promoted peel coloration by increasing the contents of Ca and Mg.