Composite moisture holding agent of humic acid and preparation method

The present invention provides a method for preparing compounded type humic acid water-retaining agent. Said method includes the following steps: adopting acrylic acid, starch and potassium hydroxide as main agent, compounding humic acid protective function group, controlling by items, respectively modifying and improving humate and potassium polyacrylate water-absorbing resin to make both them have reaction activity, then uniformly mixing them, and under the condition of heating and melting them making them implement compounding reaction so as to obtain the invented water-retaining agent with the function of promoting plant rooting, germination and growth.