By compounding rice straw with phenolic resin (PF) foam, to improve the shortcomings of PF foam itself, such as high brittleness and poor mechanical strength, and to investigate the effects of length (8 cm, 12 cm and 16 cm) and form (cross-cutting straw, slope-cutting straw and grinding straw fiber) of rice straw on the physical properties, mechanical and combustion properties of the composite material. The results show that the inner and outer surfaces of rice straw have an obvious mechanical engagement with PF foam; the bending strength, compressive strength and tensile strength perpendicular to the board surface of rice straw/PF foam composite are better than PF foam; the bending strength of 16 cm long slope-cutting rice straw/PF foam composite reaches 1.18 MPa, which is 195% higher than PF; The compressive stress at 10% strain and tensile strength perpendicular to the plate surface of 16 cm long grinding rice straw/PF foam composite were 251.30 kPa and 121.26 kPa, respectively, which were 112.1% and 20.7% higher than PF. The vertical combustion and limited oxygen index test (LOI) results showed that PF foam has better wrapping effect on straw, the thermal stability of the composite was almost the same as that of PF foam, with almost no change in oxygen index value. The flammability test results of both rice straw/PF foam composite and PF foam meet the requirements of B1
class building materials, which shows an excellent fire resistance. To sum up, 8 cm slope-cutting rice straw reinforced PF foam composite has an optimal integrated mechanical property.