Using a sample of 10 billion J/psi events collected with the BESIII detector, the decays eta' -> pi())pi(-)pi())pi(-), eta' -> pi())pi(-)pi(0)pi(0 )and eta'-> 4 pi(0 )are studied via the process J/psi -> gamma eta'. The branching fractions of eta'->pi())pi(-)pi())pi(- )and eta'->pi())pi(-)pi(0)pi(0 )are measured to be(8.56 +/- 0.25(stat)+/- 0.23(syst))x10(-5 )and (2.12 +/- 0.12(stat)+/- 0.10(syst))x10(-4), respectively, which are consistent with previous measurements but with improved precision. No significant eta'-> 4 pi(0 )signal is observed, and the upper limit on the branching fraction of this decay is determined to be less than 1.24x10(-5 )at the 90% confidence level. In addition, an amplitude analysis of eta'->pi)pi-pi)pi-is performed to extract the doubly virtual isovector form factor alpha for the first time. The measured value of alpha = 1.22 +/- 0.33(stat) +/- 0.04(syst), is in agreement with the prediction of the vector meson dominance model.