In order to study the temperature distribution along the porous pipes, the vertical temperature gradient in space below greenhouse canopy and the relation between temperature gradient and its main influencing factors on the basis of heat dissipation of pores, the heating system of greenhouse canopy with hot blast based on porous pipes was established with inlet temperature, inlet pressure and diameter of outlet as the experimental factors. Through thermal insulating porous pipes, the temperature of the front outlets, middle outlets and end outlets of porous pipes and its distribution in vertical space were measured. The results showed that the outlet temperature decreased along the porous pipes, while the temperature in vertical space decreased after an increasing trend. Under different inlet temperatures and inlet pressures, the temperature in 800～1200 mm height space of thermal insulated room rose 2.5～6.2℃.