The invention relates to a method for growth of compound cadmium sodium borate crystal; according to the method, the compound cadmium sodium borate crystal is prepared as follow: mixing compound cadmium sodium borate with cosolvent B2O3-R system or Na2B4O7, heating, performing homoiothermy, cooling to obtain a cadmium sodium borate and cosolvent mixed molten liquid, putting seed crystals loaded on a seed crystal rod in the prepared mixed molten liquid, simultaneously rotating the seed crystal rod, cooling, and then slowly cooling to obtain a required crystal, lifting the crystal off from the liquid surface, and cooling to the room temperature to obtain the compound cadmium sodium borate crystal. The method has the advantages of fast growth and low cost, the Na2Cd7B8O20 crystal with the size of 20mm * 20MM * 10mm and high optical quality can be grown, and the crystal obtained through the method is good in mechanical performance and not easy to break and deliquesce and is easy to process.