Abstract: Root architecture, or the spatial configuration and distribution of root systems in the growth medium, is closely related to P cquisition efficiency. Understanding of root architecture may provide scientific basis of genetic improvement of P efficiency in plants. For a long time, attempts have been made to quantify root architecture and to establish a comprehensive criterion which can quantitatively describe the three_dimentional root architecture. Results from experiments indicate that changes in root architecture are mainly accomplished through root gravitropic sensitivity and carbon allocation between shoot and root, hence affecting phosphorus acquisition efficiency. Root gravitropic responses are adaptive, inheritable traits induced by low phosphorus availability and other factors. Evidence exists for a genetic regulation of gravitropic responses to low phosphorus availability, with possible involvement of ethylene as a hysiological regulator. To date quantitative trait loci (QTLs) conferring root architectural characteristics have been identified in some plants, offering hopes for molecular improvement of this trait. As modern technologies advance, great breakthrough is expected for root architectural research in the future.