In this paper, we compare and analyze the superiority of k-mer segmentation and BPE subword tokenization methods based on previous studies that regard DNA sequences as languages and apply the Transformer model. We train 3-, 6-, 12-, and 24-layer Transformer encoders using k-mer segmentation with k=1, 3, 4, 5, and 6, BPE vocabulary with a token size of 4,096, and three positional encoding methods, sinusoidal, AliBi, and RoPE, and evaluate them on the GUE benchmark dataset. The experimental results show that BPE reduces the sequence length by compressing frequent motifs into variable-length tokens and improves the model generalization performance, resulting in higher and more stable performance. Among the positional encoding methods, RoPE is excellent at capturing periodic motifs and extrapolating them to long sequences, and AliBi performs well in tasks based on local dependencies. Experimental results on the number of layers show that the performance improvement is remarkable when increasing from 3 to 12 layers, and insignificant improvement or overfitting phenomenon is observed at 24 layers. This study provides practical guidance on the design of tokenization and positional encoding of DNA Transformer models.