The invention discloses an isovolumetric cutting speed calculation method for a multi-line cutting machine. The isovolumetric cutting speed calculation method for the multi-line cutting machine is realized by solving a feeding speed of any positional point during the multi-line cutting. The feeding speed of any point is obtained according to the formula as follows: F=C*P/[(R<2>-(R-h)<2>)<1/2>*(dw+2*d)*L*K], wherein F is the feeding speed, C is a cutting volume in a unit time, P is a slot pitch of a main roller, R is a radius of a cut material, h is a cutting depth, dw is a diameter of a cutting line, d is a diameter of a cut abrasive material, L is a length of the cut material and K is a safety coefficient. A maximum feeding speed Fmax is set and if the feeding speed F of one positional point, calculated through the formula, is greater than the Fmax, the Fmax is taken as the feeding speed. The isovolumetric cutting speed calculation method for the multi-line cutting machine, disclosed by the invention, has the advantages of guaranteeing the volume amount removed in a unit time as the setting value, adjusting the cutting speed F according to the slot pitch P of the main roller, the cutting position h, the cutting length L, the diameter d of the cut abrasive particle and the like and improving processing efficiency.