With the addition of Si to replace some P,Pd_(40.5)Ni_(40.5)Si_xP_(19-x)(x=0,2.5,5,9.5,14,and 19 in atomic number fraction) bulk glassy samples with the diameter of about 5 mm were successfully prepared by use of flux treatment and water quenching technology.With the increase of Si content,the glass forming ability of Pd_(40.5)Ni_(40.5)Si-xP_(19-x) increases first for low Si content and then decreases for high Si content (Si≥9.5at%).The Pd_(40.50Ni_(40.5)Si_5P_(14) glassy alloy possesses the largest supercooled liquid region△T of 119 K,the largest reduced glass transition temperature of 0.621,and the largestγparameter of 0.460,indicating that this glassy alloy possesses very large glass forming ability and very high thermal stability. With the addition of Si to replace some P, Pd_ (40.5) Ni_ (40.5) Si_xP_ (19-x) (x = 0,2.5,5,9.5,14 and 19 in atomic number fractions) of about 5 mm were successfully prepared by use of flux treatment and water quenching technology. By the increase of Si content, the glass forming ability of Pd_ (40.5) Ni_ (40.5) Si-xP_ (19-x) content and then decreases as high Si content (Si ≧ 9.5 at%). The Pd_ (40.50Ni_ (40.5) Si_5P_ (14) glassy alloy possesses the largest supercooled liquid region ΔT of 119 K, the largest reduced glass transition temperature of 0.621 , and the largest gamma parameter of 0.460, indicating that this glassy alloy possesses very large glass forming ability and very high thermal stability.