Star formation rates in distant radio galaxies are crucial for understanding the evolution of galaxies. Most processes at works in these targets observed at the most remote epochs are directly or not related to primeval sources of star formation: interplays of starbursts and AGNs, interactions of radio jets with environmental clouds. cooling flows, metal enrichment and dust distributions. Signatures of typical star formation (emission line ratios, equivalent widths, stellar continua) are observed in distant galaxies. However in most cases, they are superimposed to signatures of other processes (shocks, AGN light scattering). in particular at high z with the decrease of angular resolution and surface brightness. A larger variety of environmental components (lobes, jets, clouds and nucleus) simultaneously contribute to the global emission. So that to separate the varions emission processes becomes rapidly essential with higher distances. The 3D spectroscopy is unique to disentangle the various physical processes triggering star formation at high redshifts. Shocks and regions photoionized by the central AGN are identified from their typical features and may be localized in the various zones of the radio galaxy extended to its environment. We present results of a long term observationnal prograin with the successive Integral Field Units (IFU) TIGER and OASIS at CFHT. The present sample consists of three galaxies of increasing z: 3C 171 {z = 0.238), 3C 435A (z = 0.470) and 4C 41.17 (z = 3.8). Line ratios, continua and velocity fields are locallv measured. Interpretations of emission line ratios, velocity fields, equivalent widths, are possible with a coupled code based on CLOUDY and MAPPINGSIII results, as proposed by Moy et al. (2000, 2001). Stellar and nebular continua are interpretcd with the help of our evolutionary synthesis model PEGASE2. Ail models take into account metallicity effects.