Based on experiment of potcultivating with foliage spraying for main varieties of pineapple(var.yellow Mauritius),effects of nitrogen forms on the vegetative growth and chlorosis of pineapple were investigated so as to provide reference for rational application of nitrogen fertilizer for pineapple.The results showed that the biomass of roots,stem and leaves of pineapple by foliage spraying nitrate nitrogen was significantly lower than that by foliage spraying ammonium nitrogen or amide nitrogen,but the number of pineapple chlorosis leaves was more than that by foliage spraying ammonium nitrogen or amide nitrogen.Compared with ammonium nitrogen treatment,nitrate nitrogen treatment decreased total number of pineapple leaves,number of roots,the weight of roots,the weight of stem and leaves by 18.7%,26.5%,49.7%,43.5%,respectively,and increased number of yellow leaves by 192.7%.The main mechanism of nitrate nitrogen inhibiting the vegetative growth of pineapple was that nitrate nitrogen significantly increased the value of pH in soil,and significantly decreased Fe absorption and total Fe,active Fe,chlorophyll content of pineapple leaves(decreasing by 25.9%,66.9%,23.2% compared with ammonium nitrogen,respectively).