Abstract A study of magnetic properties in the insuluing spinel system CoxZn1-x(FeyCr1-x2O4 has been made based on the temperature relationships of the low-frequency, weak field ac susceptibilities and low field magnetizations measurements. According to the above experimental results, we propose a probable magnetic phase diagram of the spinel. This magnetic phase diagram shows the reentrant spin glass phenomena in quite wide concentration ranges in the spinel. Increasing the concentration of the magnetic ions, the freezing temperatures of the reentrant spin glass increase. These properties are common in the systems with a few kinds of the magnetic ions or the magnetic ions which concentration are quite high. The mechanism of reentrance of spin glasses has been discussed in the paper. The reentrant spin glass in the spinel is a mixed state of spin glass and ferrimagnetic microdomains or spin clusters, which come from the collapse of the ferrimagnetic state.