Through the change of welding heat input,the effect of welding heat input on the mechanical properties and microstructure of weld metal of low alloy high-strength steel CHE607 QR for spherical vessel was investigated by metallographic microscope.The result shows that,the low temperature impact performance of the weld increases first and then decreases with the increase of the welding heat input.When the welding heat input is up to 49 k J/cm,the low temperature impact of weld seam occurs;the heat input of welding is less than 42 k J/cm,the low temperature impact performance of the welding seam is better.