Bamboo fiber concrete is a type of architectural material. Because of its fast growth and environmental protection, bamboo fiber concrete attracts much attention from researchers and industries. However, research on bamboo fiber concrete is not enough which greatly affects its applications in engineering. Based on the splitting tensile test of bamboo fiber concrete, the formulas of splitting tensile strength are presented using composite material theory and fiber spacing theory respectively. A comparison of the theoretical values of splitting tensile strength with those of test is made. It is found that the formula deduced from composite material theory leads to severe errors because of its unrealistic hypothesis. Therefore the composite material theory is inappropriate to explain the strengthening mechanism of bamboo fiber concrete. On the other hand, fiber spacing theory not only has higher accuracy but also reflects the effect of fiber content and length-radius-ratio on the splitting tensile strength of concrete. So the fiber spacing theory is adapted to study the strengthening mechanism of bamboo fiber to concrete.