A highly sensitive transient absorption spectrometer was developed in this work using a nanosecond pulse diode laser as a pump source, and rapid and high sensitivity transient absorption(∆A<5×10^-6) was achieved by using the balanced detection, the timing structure of macro-pulse andmicro-pulse and an electronic delay scheme to avoid repetitive balancing. Then, the carrier dynamics of methylammonium lead iodide (MAPbI₃) thin film perovskite materials at different pump power densities were measured using the developed spectrometer, and pump power density-dependent dynamic phenomena were observed. Especially, the measurement of carrier dynamics in the linear response region was achieved at low carrier concentrations. Furthermore, the carrier dynamics of MAPbI₃ at 296 K and 220 K were measured and compared, and it was found that the carrier lifetime was extended at low temperature due to the reduction of charge recombination assisted by ionization impurities. The highly sensitive transient absorption method proposed in this work can be extended to full nanosecond pulse diode laser systems, which will not only reduce the cost of transient absorption spectrometers but also have the potential applications in rapidly evaluating the intrinsic properties of materials at low carrier densities under solar illumination.