介词by可以用来表示方位、时间、手段等，它的用法很多,下面是介词by的用法归纳：
1、by+地点名词。表示场所、方位，意为：“在…旁边”。如：
by the lake/river/tree/window/door等
She searched the top of the hill and stopped to rest on a big rock by the side of the path.(NMET90)她搜索了山顶，然后停下来在路边的一块大石头上休息。
After supper she would sit down by the fire,sometimes for as long as an hour,thinking of her young and happy days.(2003上海·春）晚饭后，她常坐在火旁，有时长达一个小时地回忆她那青春、快乐的年代。
此时要注意它与介词near有所不同，即by 表示的距离更“近”。比较：
He lives by the sea. 他住在海滨。
He lives near the sea. 他住在离海不远处。
注：有时可表:“从…旁经过”,多与动词go/walk/pass等连用。
As we boys were rushing towards the playground,Jim slipped by the table.(NMET92完形）当我们这些男生冲向操场时，吉姆从桌旁溜过。
二、by+时间名词。意为：“到…时（已发生某事），此时谓语多用完成时；最晚、不迟于…，在…之前”。如：
by now/then/this time/next Friday/the end of/three o`clock等。
By the end of last year,another new gymnasium had been completed.(2003上海·春）到去年年底，又有一座新体育馆峻工了。
The train leaves at 6:00 pm.So I have to be at the station by 5:40 pm at the latest.(NMET97)火车下午六点开，所以最晚我得五点四十赶到车站。
三、by+名词。可用来表方法、方式、手段等。
1、by+the+可数的时间、长度、重量等名词。意为：“按…计算，按…买(卖)”。如：
by the pound/ton/yard/meter/dozen/bale/day/month等。
Cleaning women in big cities usually get paid by the hour.(NMET98)城市里的女清洁工通常按小时获得报酬。
In the market,tobacco is sold by the bale,eggs by the dozen and salt by the pound.在市场里，烟叶按捆卖，鸡蛋按打卖，盐按磅卖。
2、by+表示时间、长度、重量等总称的不可数名词（名词前不加冠词）。意为：“按…计算，按…买(卖)”。如：
by time/volume/length/weight/height/depth/width/area等。
As we all know,the freight of the luggage is charged by weight.众所周知，行李的运费是按重量计算的。
3、by+交通工具、交通方式名词（名词前不加冠词，不变复数）。意为：“通过…，由…，乘…”。如：
by train/rail/tube/taxi/bus/truck/bike/boat/plane;by land/road/sea/water/air等。（on foot)
It takes a long time to go there by train;it`s quicker by road.(或by bus)(NMET93)乘火车去那儿要花很长时间，公路比较快。
“I usually go there by train”.“Why not try going by boat(或water)for a change?”(NMET92)“我常乘火车去那儿。”“为何不尝试一下坐船呢？”
4、by+抽象名词或具有抽象意义的普通名词（名词前不加冠词，不变复数）。意为：“靠…，通过…，由…所致”。如：
by skill/determination/practice/diligence/inference/chance/accident;by mail/letter/radio/fax/telephone/telegraph/hand/machine等。
Although he had been searching in the wrong area most of the time,he found it by logic,not by luck.
(NMET2002阅读）虽然他曾大部分时间一直在错误的地方寻找，但他还是靠逻辑推理而非运气，找到了它。
I made a coat with my own hands.It was made by hand,not by machine.
我用双手织了一件外套。它是用手工织的，而不是机器织的。
5、by+ 地点或工具等具体名词。表路线、途径，意为：“通过（某物、某地），取道…”。如：
by a stone bridge/the back door/the freeway/country roads等。
The man entered the room by the back door.那人通过后门进入了房间。
6、by+动词—ing.意为：“通过…，靠…，凭…”。如：
by waiting/practing/begging/working/imitating等。
He gained his wealth by printing works of famous writers.(NMET95)他通过印刷著名作家的作品而获得了巨大的财富。
Our bodies are strengthened by taking exercise. Similarly,our minds are developed by learning.(2000上海)身体是靠锻炼强壮的，同样，大脑是靠学习开发的。
四、by+数量词。
1、表升降、增减的程度。如：by one-fifth/20 percent/￡3/two feet等。
With production up by 60%,the company has had another excellent year.(NMET2000)产量上升了百分之六十，这家公司今年的业绩极好。
The demand for organic food is increasing by about one third every year.(NMET2002阅读)对绿色食品的需求每年在增长大约三分之一。
2、表示距离和面积、体积中的尺寸及乘除法中的运算。如：by 2cm/6 inches/four feet/nine yards/a hair`s breadth等。
Luckily,the bullet narrowly missed the captain by an inch.(2002上海）幸运地是，那颗子弹差一英寸就击中了上尉。
The bed is three meters wide by two meters long,and can fit at least four at one time.(NMET2001阅读)那张床三米宽，两米长，一次至少可以睡四个人。
五、by+身体部位名词或衣服名词。表示被抓住身体/衣物的某一部分，常与动词catch/seize/take/hold/grab等连用。如：
by the hair/hand/arm/nose/horns;by the collar/lape/sleeve等。
The policeman caught the thief by the arm.警察抓住了小偷的胳膊。
The soldier grabbed the child by the collar.那个士兵揪住了孩子的衣领。
六、by的常见短语：
by means of 依靠; 将; 借助于;
by way of 路经; 途经; 作为; 意在;
by the way 顺便地，附带说说;
one by one 逐一; 一个接一个;
step by step 一步步地，逐步地，逐渐地;
side by side 并排; 肩并肩地，一起; 相互支持;
shoulder by shoulder 肩并肩;
by oneself 自行; 单独，独力; 孑然一身;
by birth 在血统上，生来;
by society 于社会; 被社会;
take…by surprise 使...大吃一惊
learn…by heart 用心去学
what do you mean by … 你这是什么意思;
by my watch 靠我的表(看的时间)
等。