In this paper,the generation of stage shaped pulses in thulium fiber lasers based on nonlinear polarization rotation mode locking is investigated.By introducing a segment of SMF 28 fiber with a length of 100 m and 350 m respectively before and after the nonlinear polarization rotation mode locking device to enhance intracavity nonlinearity and accumulate negative dispersion,a dual wavelength (wavelengths of 2025 nm and 2034 nm,respectively) step shaped pulse with a base width of 50 ns,a repetition frequency of 615.6 kHz,and a signal to noise ratio of 55 dB is obtained,and it is found that carefully adjusting the polarization controller and changing the pump power can finely adjust the shape of step shaped pulses.Through the study,it is found that the stepped pulse is formed by the combination of two rectangular pulses,and the front and rear pumps have different influences on the two rectangular pulses,and the energy can be realized by changing the polarization state between the front and rear two rectangular pulses.The experiment provides a good experimental platform for studying the pulse dynamics and pulse shaping of passive mode locked fiber lasers.