NOVELTY - Preparing alkaline earth fluorochloride up-conversion luminous nanocrystals comprises adding alkaline earth trifluoroacetic acid compound (I), oleic acid and octadecene into three necked flask, heating under the protection of nitrogen gas atmosphere, deaerating, heating to obtain alkaline earth fluoride nanocrystal, cooling, and adding trichloroacetic acid compound, oleic acid and octadecene mixture, heating, continuously heating to obtain alkaline-earth fluorochloride (IV) or rare earth doped alkaline earth fluorochloride nanocrystals, washing with ethanol cyclohexane mixture, and drying.    USE - The nanocrystal is useful in lighting display, solar cells and biological markers.    ADVANTAGE - The nanocrystal has high yellow up-conversion luminescence properties.    DETAILED DESCRIPTION - Preparing alkaline earth fluorochloride up-conversion luminous nanocrystals comprises: (a) adding 0.1-1 mmol alkaline earth trifluoroacetic acid compound of formula (M(CF3COO)2) (I), oleic acid (10 ml) and octadecene (10 ml) into 100 ml three necked flask, heating to 100 degrees C under the protection of nitrogen gas atmosphere, maintaining for 30 minutes and deaerating and removing water, continuously heating to 260-310 degrees C under nitrogen atmosphere, maintaining for 1-6 hours to obtain alkaline earth fluoride nanocrystal of formula (MF2) (II), where a rare earth ion is added in the solution of trifluoroacetic acid compound of formula (Ln(CF3COO)3) (III), (b) cooling nanocrystal solution of (II) to room temperature, and immediately adding 0.1-1 mmol trichloroacetic acid, oleic acid (10 ml) and octadecene (10 ml) mixture, heating to 100 degrees C under the protection of nitrogen gas atmosphere, maintaining for 30 minutes and deaerating and removing water, continuously heating to 120-280 degrees C under nitrogen atmosphere, maintaining for 30 minutes to obtain alkaline-earth fluorochloride compound of formula (MFCl) (IV) or rare earth doped alkaline earth fluorochloride (Ln:MFCl) nanocrystals, and (c) washing with ethanol cyclohexane mixture, and drying at 40-80 degrees C.    M = Ca, Sr or Ba; and    Ln = Er or Yb.