The work aims to research the grating anti-counterfeiting technology of phase modulation based on splice latent images embedded into sub-channels according to the working principle of difference in hidden and extraction effects caused by different channels in which the latent image information was embedded. The butterfly-like latent image was divided into two symmetrical parts. As to the four channels of CMYK, two channels of them could form a group and be respectively embedded into both parts, so as to seamlessly splice and form the complete anti-counterfeit information. The concealment of the latent image as a whole was evaluated in subjective and objective methods to prove the non-applicability of channel K. Digital grating corresponding to the host image with different number of screening lines was designed to extract the hidden information. In such case, the conspicuousness of latent images was good. Sub-channel splice latent image method had good anti-counterfeiting effects. When both parts of the latent image were respectively located at channels C and M, their concealment and extraction conspicuousness were the best. Channel K was not suitable to be used as the embedded channel of anti-counterfeiting information. The number of screening lines of host image had no significant impact on the anti-counterfeiting effects of the splice latent image. In conclusion, this study provides a reference method for two channels. It can increase process complexity, strengthen the anti-counterfeiting effects and provide new theory for the latent image anti-counterfeiting technology of phase modulation.