By studying the influence of the combination of humic acid and urea on the conversion of urea in soil，this paper provides a scientific basis for the selection of the production process of humic acid urea. Soil cultivation test was conducted on fluvo-aquic soil，and 8 treatments were set up:without urea(CK)，the common molten urea(U)，0.5% of added amount of humic acid humic acid(HA0.5)，5% of added amount of humic acid(HA5)，0.5% humic acid added amount mixed with urea(HA+U0.5)，0.5% humic acid added amount to the molten urea humate(HAU0.5)，5% humic acid added amount mixed with urea(HA+U5)，5% humic acid added amount to the molten urea humate(HAU5). The urea residue，ammonium nitrogen content，nitrate nitrogen content，soil pH value and soil urease activity during the conversion process were analyzed. The results showed that:(1)Compared with U，humic acid with urea reduced ammonia volatilization by 23.5% on average. When 5% humic acid was added，melting humic acid and urea significantly reduced the accumulation of ammonia volatilized nitrogen by 13.5% compared with mixing humic acid and urea.(2)Both humic acid and urea prepared by the two processes slowed down the hydrolysis of urea to a certain extent. On the whole，the residues of urea treated with humic acid with urea were 29.2%，22.0%，10.3% and 11.8% higher than those of U at 0.25，0.5，1 and 2 d after cultivation. The residue of urea treated by melting humic acid and urea was 21.3%～50.8% higher than that of mixed humic acid with urea.(3)At the end of cultivate，compared with U，humic acid with urea increased the mineral nitrogen content by 3.8%～12.6%；Compared with mixed humic acid and urea，melting humic acid and urea increased mineral nitrogen by 7.6%～13.8%.(4)On the 0.25 and 0.5 d of cultivation，compared with U，the mixed humic acid urea reduced the urease activity by 19.1% and 12.3%，while the fused humic acid urea significantly increased the urease activity by 48.5% and 102.1%. The above results showed that humic acid could reduce ammonia volatilization and slow down urea hydrolysis no matter by which process it combines with urea，and the effect of melting process is more obvious than mixing process.