Abstract: A laboratory study was conducted to investigate the effect of operating pressure on the discharge characteristics of porous pipe as micro-irrigation laterals with different specifications. Experimental results showed that emission rates for both pipes decreased drastically during the initial test stage. Exponential relationship between emission rate and operating pressure was observed within the testing pressure range of 0～70 kPa. Minimum emission rate variation coefficients were reached for both pipes within the operating pressure range of 50～60 kPa. It can be concluded that operating pressure has significant effects on emission rate and emission uniformity of porous pipe. In general, the larger diameter pipe shows better discharge characteristics than the smaller one.