A co-located 3He and 129Xe nuclear spin free precession measurement at sub-μT magnetic field was carried out in a magnetically shielded environment. The uncorrected quotient of the gyromagnetic ratios between neutral 3He and 129Xe atoms is determined to be 2.754 082 81(07), accounting for only statistical error. Our measurement shows that this ratio has a stability of 1.4×10-5/ √τ, demonstrating the ability to reach the current precision limit of the quotient in a 10000 s of averaging time τ. This precision is enough for the next-generation EDM search in neutral 129Xe atoms based on a similar comagnetometer scheme.