Ambient LoRa backscatter enables long-range communication due to its long-period symbol. Most of the existing works struggle to balance range and throughput: systems with symbol-level modulation offers long transmission range at the cost of low data rate, while systems with high modulation efficiency suffer from limited transmission distance due to weak signals. We propose SubLoRa, which significantly improves throughput while maintaining long-range communication. SubLoRa achieves the high-rate modulation by the proposed Subchirp Frequency Offset Modulation (SFOM), which divides a chirp into multiple subchirps each being shifted by frequency. We propose a prewaveform sampling strategy that enables SFOM with low power. For decoding, we propose a Frequency-Difference Recombination of Chirp (FDRC) demodulation based on time-domain correlation, which enables reliable decoding of low-power signals in long-range links. We implement SubLoRa and conduct extensive evaluation. The results show SubLoRa can achieve up to 29.66× throughput gain and 7.54× throughput gain compared with the State-Of-The-Art (SOTA) LoRa backscatter system PLoRa and Pacim, respectively.