The invention discloses a transimpedance amplifier applied to a high-speed optical receiver and a design method. The transimpedance amplifier comprises a three-level high gain amplifier A and a feedback resistor Rf. The three-level high gain amplifier A comprises a first-level amplifier A1, a second-level amplifier A2 and a third-level amplifier A3. The output end of the first-level amplifier A1 is connected with the input end of the second-level amplifier A2. The output end of the second-level amplifier A2 is connected with the input end of the third-level amplifier A3. Two ends of the feedback resistor Rf are connected with the input end of the first-level amplifier A1 and the output end of the third-level amplifier A3. According to the transimpedance amplifier, a structure of reducing bandwidth and then increasing the bandwidth is employed in the amplifier of the TIA (Transimpedance Amplifier), so under the condition of ensuring the bandwidth required by a system transmission rate, the transimpedance gain of the TIA is improved, and the equivalent input noise of the TIA is reduced.