跟踪了一下代码，发现，是代码有点问题：

com.alibaba.otter.canal.client.adapter.es7x.support.ES7xTemplate类的delete方法:

    @Override
    public void delete(ESMapping mapping, Object pkVal, Map<String, Object> esFieldData) {
        //处理配置了_id
        if (mapping.get_id() != null) {
            ESDeleteRequest esDeleteRequest = this.esConnection.new ES7xDeleteRequest(mapping.get_index(),
                pkVal.toString());
            //构造的是一个Delete的对象
            getBulk().add(esDeleteRequest);
            commitBulk();
        } else {//处理没有配置_id，但是配置了pk为主键的配置
            ESSearchRequest esSearchRequest = this.esConnection.new ESSearchRequest(mapping.get_index())
                .setQuery(QueryBuilders.termQuery(mapping.getPk(), pkVal))
                .size(10000);
            SearchResponse response = esSearchRequest.getResponse();
            for (SearchHit hit : response.getHits()) {
                ESUpdateRequest esUpdateRequest = this.esConnection.new ES7xUpdateRequest(mapping.get_index(),
                    hit.getId()).setDoc(esFieldData);
                //构造的是一个Update的对象
                getBulk().add(esUpdateRequest);
                commitBulk();
            }
        }
    }

我试验了下，只需要修改Es7xUpdateRequest为Es7xDeleteRequest就可以了！修改如下:

@Override
    public void delete(ESMapping mapping, Object pkVal, Map<String, Object> esFieldData) {
        if (mapping.get_id() != null) {
            ESDeleteRequest esDeleteRequest = this.esConnection.new ES7xDeleteRequest(mapping.get_index(),
                pkVal.toString());
            getBulk().add(esDeleteRequest);
            commitBulk();
        } else {
            ESSearchRequest esSearchRequest = this.esConnection.new ESSearchRequest(mapping.get_index())
                .setQuery(QueryBuilders.termQuery(mapping.getPk(), pkVal))
                .size(10000);
            SearchResponse response = esSearchRequest.getResponse();
            for (SearchHit hit : response.getHits()) {
                ESDeleteRequest esDeleteRequest = this.esConnection.new ES7xDeleteRequest(mapping.get_index(), hit.getId());
                getBulk().add(esDeleteRequest);//修改为ES7xDeleteRequest类型就能删除了
                commitBulk();
            }
        }
    }

查看了下ES6也存在这个问题，一样修改就行了，对于配置_id的没有任何问题