The structural relaxation of Zr55Cu30Al10Ni5 bulk amorphous alloy during annealing at 360 and 380℃ have been investigated by in-situ synchrotron radiation x-ray small angle scattering (SAXS). The experimental results o btained show that the fluctuations of electron density during the annealing proc ess are due to structural relaxations of bulk amorphous alloy before cyrstalliza tion. It is found that a homogenization in electron density takes place during a nnealing, which is attributed to the change from topological short-range order (TSRO) structural relaxation to chemical short-range order (CSRO) structural relaxation. The annealing time required for this change becomes shorter as the annealing temperature increases.