Bandwidth,gain and gain-flattening of Raman fiber amplifier(RFA) directly impact on the transmission quality of fiber communication system. RFA with two-pump cascade tellurite fiber was put forward that it will aim for optimizing these parameters according to the features of tellurite fiber Raman gain spectrum(RGS). And the constraints of fiber lengths and pumping parameters were derived when achieving gain-flattening. Quintic polynomial fitting on RGS can accurately reflect the information of RGS and simplify the conditions of achieving gain-flattening. Through Matlab simulation verification,when the two fibers are respectively 0.339 km and 0.16 km, the peak gain is 17.81 dB, gain-flattening is 0.66 dB, and amplified bandwidth is 48 nm. This project supplies a new approach for designing RFA with wide bandwidth, high gain and low gain-flattening.