A set of laser oscillations of four strontium atom spectral lines simultaneity have been obtained, through high-repetition-frequency pulsed discharge in mixed gases of strontium vapor and helium buffer gas. The corresponding wavelengths with the transitions from compound three-energy levels 4d·3D3,2,1 to 5p·3P02,1,0 are 2.92μm, 3.01μm, 2.69μm and 2.60μm respectively,their ratios of intensities are 5∶4∶4∶1 and the total average laser power is 10mW.As far as we know,the laser spectral lines have never been reported except 3.01μm.On the basis of analyzing characteristics of corresponding energy levels and experimental phenomena,the action mechanism is discussed primarily.We suggest the classification of the spectral lines to be named as M-M transition laser.