For actual multipath channels, inter symbol interference (ISI) may seriously degrade LoRa performance. With the path overlapping interference analyzed, the upper bound of LoRa bit error rate (BER) has been approximated. Then we propose a block interleaved chirp spreading LoRa (BICS-LoRa) modulation to split the multipath interference into small ones at different positions. The probability of interference peak being greater than the direct path peak is reduced, so does the BER. Experiment results show BICS-LoRa can reduce the peak of multipath interference and may result in BER reduction. Besides, the performance gain increases with SF value in most cases.