Hi, Is it possible to draw and generate GDS of resistor of resistance below 2000 ohm?

Considering there are limits for the resistor length and width, you can always draw resistors in parallel. Normally, resistors are defined by resistance per square. You can make any resistance, as far as the area allows. Of course, remember that metal tracks and contacts also have a resistance.

@Vyshnav P Dinesh: Because the terminal resistance is less well controlled, if you want a reasonably accurate resistor, you should have L >> W. But even among the poly resistors (assuming we're talking about sky130), you can choose between (approximately) 50 ohms/square, 300 ohms/square, and 2000 ohms/square. The most well-controlled of all the resistor types is the ~300 ohms/square. To ensure that all resistors have L >> W (at least, say, a factor of 5 to 10), choose the appropriate resistor type, and as Luis said, combine resistors in parallel if necessary.

for poly resistors if w/l=1, then resistance is 2000ohms, if i change to l>>w resistance increasing. I do not want to use 40 poly res(parallel) for making an 50ohm resistance. what should i do?

First of all, you must be extra careful while routing to this 50 Ohm resistor. The metal tracks and contacts could have resistances in this order of magnitude. If you use a L of 0.5 um, you would need a 20 um W. This is small. Maybe even too small.

then how can i ensure l>>w as Tim said

It depends where your contacts are. If you really want to have an accurate resistor, you should use the ones modelled by the foundry. Then you use parallel resistors. You could have a row of contact of 0.5 x 20. A row of high resistive poly. Then another row of contacts. How much resistance will have that row of contacts, that I don't know.

@Vyshnav P Dinesh: High-resistance poly is not intended for the use of making 50 ohm resistors. The basic poly resistor is around 50 ohms per square; local interconnect is about 12 ohms per square. These would be the best choices; but as Luis mentioned, contact resistances are very high. For that reason, probably local interconnect is the best choice because the contacts to metal1 are 9 ohms each, making it easier to get the resistor's terminal resistance below 1 ohm. The poly contacts are ~150 ohms each, so for any poly resistor your terminal resistance is going to be a significant portion of the total.