Abstract: Efficient use of photosynthetic active radiation (PAR) is a major yield advantage factor in relay intercropping. This study therefore analyzed the dynamic processes of leaf area index (LAI) and the interception and utilization mechanisms of PAR in a relay intercropping system of maize and capsicum. Three treatments (sole cropping maize, sole cropping capsicum, and relay intercropping maize/capsicum) were set up. The study shows that though LAI for relay intercropping maize/capsicum is slightly lower than that for sole cropping maize and sole cropping capsicum, it exhibits a uni-peak curve for the three cropping systems. Under relay intercropping with maize, capsicum canopy light extinction coefficient (k) decreases. There is a significant difference in intercepted PAR between maize/capsicum relay intercropping and maize or capsicum sole cropping. The PAR intercepted amounts under maize/capsicum relay intercropping system is 42.25% higher than the weighted mean of PAR for maize and capsicum sole cropping according to their relay intercropping proportion (0.788∶0.222). PAR use efficiency under maize/capsicum relay intercropping system is 39.51% higher than the weighted mean for maize and capsicum sole cropping. Dry-matter accumulation rate for relay intercropping maize is higher than that for sole cropping maize, whereas the opposite is the case for sole cropping capsicum. The fraction of dry-matter allocated to stems and branches in relay intercropping capsicum is slightly lower than that in sole cropping capsicum. However, the fractions of allocated dry-matter to roots and fruits in relay intercropping capsicum are respectively 2.8% and 2.6% higher than those in sole cropping capsicum. There is insignificant difference in the fractions of allocated dry-matter to the different organs between relay intercropping and sole cropping maize. The study consequently suggests that in comparison with mono-culture, high productivity of relay intercropping is fully explainable by increasing interception and use efficiency of PAR. Reasonable intercropping of crops therefore complements the interception and utilization of PAR in space and time.