In order to improve the workability of the grout for simultaneous grouting in shield tunneling, the grout proportion is optimized by adding sodium carbonate and calcium lignosulphonate. The influence of water/blinder ratio, fly ash/cement ratio, bentonite/water ratio, sodium carbonate amount, calcium lignosulphonate amount and cement amount on the grout performance is tested by orthogonal experiment. Finally, optimized grout proportion is suggested. This paper can provide reference for similar projects in the future.