A compact polarization splitter rotator （PSR） based on the principle of mode evolution is proposed. The device consists of a tapered TM₀-TE₁ mode converter and a mode splitter with an asymmetric directional coupler （ADC） structure， optimized by particle swarm optimization （PSO） and the principle of spline interpolation. The device is simulated using the finite difference time domain method （FDTD）. The numerical results show： for TE₀ mode input， a low insertion loss （<0.007 dB）， low crosstalk （<-28.7 dB）， and high polarization extinction ratio （>49.1 dB） in the 100 nm （1500~1600 nm） bandwidth is achieved within a device length of only 45μm. On the other hand， for TM₀ mode input， a low insertion loss （<0.34 dB）， low crosstalk （<-47.1 dB）， and high polarization extinction ratio （>15.5 dB） in the whole C-band is achieved. The insertion loss value at 1550 nm is reduced to 0.06 dB. In addition， the tolerance of the device is analyzed and the results reveal that the proposed device is robust. The designed PSR has small loss， compact size， and low crosstalk， which are important for future applications in large-scale photonic integration.