Porcine reproductive and respiratory syndrome virus (PRRSV) has been investigated extensively at the molecular level. Nevertheless, genome wide study on the temporal and spatial dynamics of the virus is non-existed. To explore this topic, we determined complete coding genome sequences for four PRRSV isolates and analyzed them together with 122 global published ones using the Bayesian coalescent approach as well as Bayesian inferences and maximum likelihood methods. All EU-type viruses belonged to one of two groups or were unclassified (5 isolates), and all NA-type isolates were divided into one of three major groups or were unclassified (1 isolate). Here, there was no apparent association between temporal or geographic origin and heterogeneity of global PRRSVs. Of the eight ORFs, ORF1a showed the most powerful evolutionary signal. Our findings also indicated that the PRRS virus evolved at a rate of 1.98 × 10-3 substitutions/site/year, and the most recent common ancestor of the virus existed 786.4 years ago. Here, EU-type viruses segregated 115.7 years ago, while NA-type isolates diverged 179.8 years before the present. In addition, our reconstruction of the effective population size depicted five phases of epidemic growth: an initial constant, followed sequentially by slow decrease, slight increase, sharp decline, and then a rapid expansion approaching the present.