Ultrasonic assisted method is an effective method to prepare nanomaterials,which can improve their magnetic and optical properties. Described in this paper,GdPO sub(4): Ce,Tb ternary system fluorescent powder was synthesized under different p H conditions by ultrasonic-assisted. Optical and structural properties of the fluorescent powder were determined by X-ray Powder Diffraction( XRD),Fourier Transform Infrared Spectroscopy( FTIR),Scanning Electron Microscopy( SEM),Transmission Electron Microscopy( TEM) and Photoluminesce( PL). The following conclusions are drawn:( 1) When p H = 1,synthetic samples are 15 nm x 104 nm hexagonalnanobars like orthophosphate,green phosphor. Cystals prefer growing at the face of( 102) and( 200). When p H < 1,no samples can be synthesized,whereas granular orthophosphate green phosphors were synthesized when p H > 1.( 2) A possible formation mechanism has been put forward,which provided further evidence for the fluorescent efficiency enhancement. Because the 5d energy states of Ce