The invention discloses water-soluble humic acid fertilizer and a preparation method. The water-soluble humic acid fertilizer is composed of 20-30% of bio-active humic acid, 10-15% of magnesium nitrate, 7-11% of citric acid, 8-12.5% of sodium tetraborate, 8-13% of urea, 2-8% of water-soluble monoammonium phosphate, 4-9% of potassium sulphate, 2-7% of zinc sulphate monohydrate, 1-6% of ferrous sulfate, 1-6% of thiamethoxam and 10.5-15% of hymexazol. The water-soluble humic acid fertilizer integrates the humic acid, major, medium and trace elements and pesticide, therefore, the utilization rate of lemons to the trace elements is improved, the etiolation phenomenon due to the fact that the lemons are lack of the necessary medium and trace elements is effectively improved, and meanwhile the etiolation phenomenon caused by pest and disease damage such as planococcodes robustus, thrips, root rot and damping off can be effectively controlled. According to the water-soluble humic acid fertilizer, the fast-acting property and the durability are integrated, the fertilizer application amount and the application times are decreased, soil hardening is reduced, the control effect is improved, the labor cost is lowered, the toxic effects of the pesticide on natural enemies and pollution of the pesticide to water are reduced, and the economical and biological benefits are significant.